linux.git/kernel/bpf, branch v6.12.81

bpf: Fix u32/s32 bounds when ranges cross min/max boundary

2026-04-11T12:24:55+00:00

[ Upstream commit fbc7aef517d8765e4c425d2792409bb9bf2e1f13 ]

Same as in __reg64_deduce_bounds(), refine s32/u32 ranges
in __reg32_deduce_bounds() in the following situations:

- s32 range crosses U32_MAX/0 boundary, positive part of the s32 range
  overlaps with u32 range:

  0                                                   U32_MAX
  |  [xxxxxxxxxxxxxx u32 range xxxxxxxxxxxxxx]              |
  |----------------------------|----------------------------|
  |xxxxx s32 range xxxxxxxxx]                       [xxxxxxx|
  0                     S32_MAX S32_MIN                    -1

- s32 range crosses U32_MAX/0 boundary, negative part of the s32 range
  overlaps with u32 range:

  0                                                   U32_MAX
  |              [xxxxxxxxxxxxxx u32 range xxxxxxxxxxxxxx]  |
  |----------------------------|----------------------------|
  |xxxxxxxxx]                       [xxxxxxxxxxxx s32 range |
  0                     S32_MAX S32_MIN                    -1

- No refinement if ranges overlap in two intervals.

This helps for e.g. consider the following program:

   call %[bpf_get_prandom_u32];
   w0 &= 0xffffffff;
   if w0 < 0x3 goto 1f;    // on fall-through u32 range [3..U32_MAX]
   if w0 s> 0x1 goto 1f;   // on fall-through s32 range [S32_MIN..1]
   if w0 s< 0x0 goto 1f;   // range can be narrowed to  [S32_MIN..-1]
   r10 = 0;
1: ...;

The reg_bounds.c selftest is updated to incorporate identical logic,
refinement based on non-overflowing range halves:

  ((x ∩ [0, smax]) ∩ (y ∩ [0, smax])) ∪
  ((x ∩ [smin,-1]) ∩ (y ∩ [smin,-1]))

Reported-by: Andrea Righi 
Reported-by: Emil Tsalapatis 
Closes: https://lore.kernel.org/bpf/aakqucg4vcujVwif@gpd4/T/
Reviewed-by: Emil Tsalapatis 
Acked-by: Shung-Hsi Yu 
Signed-off-by: Eduard Zingerman 
Link: https://lore.kernel.org/r/20260306-bpf-32-bit-range-overflow-v3-1-f7f67e060a6b@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Paul Chaignon 
Signed-off-by: Greg Kroah-Hartman

bpf: Add third round of bounds deduction

2026-04-11T12:24:55+00:00

[ Upstream commit 5dbb19b16ac498b0b7f3a8a85f9d25d6d8af397d ]

Commit d7f008738171 ("bpf: try harder to deduce register bounds from
different numeric domains") added a second call to __reg_deduce_bounds
in reg_bounds_sync because a single call wasn't enough to converge to a
fixed point in terms of register bounds.

With patch "bpf: Improve bounds when s64 crosses sign boundary" from
this series, Eduard noticed that calling __reg_deduce_bounds twice isn't
enough anymore to converge. The first selftest added in "selftests/bpf:
Test cross-sign 64bits range refinement" highlights the need for a third
call to __reg_deduce_bounds. After instruction 7, reg_bounds_sync
performs the following bounds deduction:

  reg_bounds_sync entry:          scalar(smin=-655,smax=0xeffffeee,smin32=-783,smax32=-146)
  __update_reg_bounds:            scalar(smin=-655,smax=0xeffffeee,smin32=-783,smax32=-146)
  __reg_deduce_bounds:
      __reg32_deduce_bounds:      scalar(smin=-655,smax=0xeffffeee,smin32=-783,smax32=-146,umin32=0xfffffcf1,umax32=0xffffff6e)
      __reg64_deduce_bounds:      scalar(smin=-655,smax=0xeffffeee,smin32=-783,smax32=-146,umin32=0xfffffcf1,umax32=0xffffff6e)
      __reg_deduce_mixed_bounds:  scalar(smin=-655,smax=0xeffffeee,umin=umin32=0xfffffcf1,umax=0xffffffffffffff6e,smin32=-783,smax32=-146,umax32=0xffffff6e)
  __reg_deduce_bounds:
      __reg32_deduce_bounds:      scalar(smin=-655,smax=0xeffffeee,umin=umin32=0xfffffcf1,umax=0xffffffffffffff6e,smin32=-783,smax32=-146,umax32=0xffffff6e)
      __reg64_deduce_bounds:      scalar(smin=-655,smax=smax32=-146,umin=0xfffffffffffffd71,umax=0xffffffffffffff6e,smin32=-783,umin32=0xfffffcf1,umax32=0xffffff6e)
      __reg_deduce_mixed_bounds:  scalar(smin=-655,smax=smax32=-146,umin=0xfffffffffffffd71,umax=0xffffffffffffff6e,smin32=-783,umin32=0xfffffcf1,umax32=0xffffff6e)
  __reg_bound_offset:             scalar(smin=-655,smax=smax32=-146,umin=0xfffffffffffffd71,umax=0xffffffffffffff6e,smin32=-783,umin32=0xfffffcf1,umax32=0xffffff6e,var_off=(0xfffffffffffffc00; 0x3ff))
  __update_reg_bounds:            scalar(smin=-655,smax=smax32=-146,umin=0xfffffffffffffd71,umax=0xffffffffffffff6e,smin32=-783,umin32=0xfffffcf1,umax32=0xffffff6e,var_off=(0xfffffffffffffc00; 0x3ff))

In particular, notice how:
1. In the first call to __reg_deduce_bounds, __reg32_deduce_bounds
   learns new u32 bounds.
2. __reg64_deduce_bounds is unable to improve bounds at this point.
3. __reg_deduce_mixed_bounds derives new u64 bounds from the u32 bounds.
4. In the second call to __reg_deduce_bounds, __reg64_deduce_bounds
   improves the smax and umin bounds thanks to patch "bpf: Improve
   bounds when s64 crosses sign boundary" from this series.
5. Subsequent functions are unable to improve the ranges further (only
   tnums). Yet, a better smin32 bound could be learned from the smin
   bound.

__reg32_deduce_bounds is able to improve smin32 from smin, but for that
we need a third call to __reg_deduce_bounds.

As discussed in [1], there may be a better way to organize the deduction
rules to learn the same information with less calls to the same
functions. Such an optimization requires further analysis and is
orthogonal to the present patchset.

Link: https://lore.kernel.org/bpf/aIKtSK9LjQXB8FLY@mail.gmail.com/ [1]
Acked-by: Eduard Zingerman 
Co-developed-by: Eduard Zingerman 
Signed-off-by: Eduard Zingerman 
Signed-off-by: Paul Chaignon 
Link: https://lore.kernel.org/r/79619d3b42e5525e0e174ed534b75879a5ba15de.1753695655.git.paul.chaignon@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Paul Chaignon 
Signed-off-by: Greg Kroah-Hartman

bpf: Improve bounds when s64 crosses sign boundary

2026-04-11T12:24:55+00:00

[ Upstream commit 00bf8d0c6c9be0c481fc45a3f7d87c7f8812f229 ]

__reg64_deduce_bounds currently improves the s64 range using the u64
range and vice versa, but only if it doesn't cross the sign boundary.

This patch improves __reg64_deduce_bounds to cover the case where the
s64 range crosses the sign boundary but overlaps with the u64 range on
only one end. In that case, we can improve both ranges. Consider the
following example, with the s64 range crossing the sign boundary:

    0                                                   U64_MAX
    |  [xxxxxxxxxxxxxx u64 range xxxxxxxxxxxxxx]              |
    |----------------------------|----------------------------|
    |xxxxx s64 range xxxxxxxxx]                       [xxxxxxx|
    0                     S64_MAX S64_MIN                    -1

The u64 range overlaps only with positive portion of the s64 range. We
can thus derive the following new s64 and u64 ranges.

    0                                                   U64_MAX
    |  [xxxxxx u64 range xxxxx]                               |
    |----------------------------|----------------------------|
    |  [xxxxxx s64 range xxxxx]                               |
    0                     S64_MAX S64_MIN                    -1

The same logic can probably apply to the s32/u32 ranges, but this patch
doesn't implement that change.

In addition to the selftests, the __reg64_deduce_bounds change was
also tested with Agni, the formal verification tool for the range
analysis [1].

Link: https://github.com/bpfverif/agni [1]
Acked-by: Eduard Zingerman 
Acked-by: Shung-Hsi Yu 
Signed-off-by: Paul Chaignon 
Link: https://lore.kernel.org/r/933bd9ce1f36ded5559f92fdc09e5dbc823fa245.1753695655.git.paul.chaignon@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Paul Chaignon 
Signed-off-by: Greg Kroah-Hartman

bpf: reject direct access to nullable PTR_TO_BUF pointers

2026-04-11T12:24:38+00:00

[ Upstream commit b0db1accbc7395657c2b79db59fa9fae0d6656f3 ]

check_mem_access() matches PTR_TO_BUF via base_type() which strips
PTR_MAYBE_NULL, allowing direct dereference without a null check.

Map iterator ctx->key and ctx->value are PTR_TO_BUF | PTR_MAYBE_NULL.
On stop callbacks these are NULL, causing a kernel NULL dereference.

Add a type_may_be_null() guard to the PTR_TO_BUF branch, matching the
existing PTR_TO_BTF_ID pattern.

Fixes: 20b2aff4bc15 ("bpf: Introduce MEM_RDONLY flag")
Signed-off-by: Qi Tang 
Acked-by: Kumar Kartikeya Dwivedi 
Link: https://lore.kernel.org/r/20260402092923.38357-2-tpluszz77@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix regsafe() for pointers to packet

2026-04-11T12:24:33+00:00

[ Upstream commit a8502a79e832b861e99218cbd2d8f4312d62e225 ]

In case rold->reg->range == BEYOND_PKT_END && rcur->reg->range == N
regsafe() may return true which may lead to current state with
valid packet range not being explored. Fix the bug.

Fixes: 6d94e741a8ff ("bpf: Support for pointers beyond pkt_end.")
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Andrii Nakryiko 
Reviewed-by: Daniel Borkmann 
Reviewed-by: Amery Hung 
Acked-by: Eduard Zingerman 
Link: https://lore.kernel.org/bpf/20260331204228.26726-1-alexei.starovoitov@gmail.com
Signed-off-by: Sasha Levin

bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR

2026-04-02T11:09:26+00:00

[ Upstream commit c845894ebd6fb43226b3118d6b017942550910c5 ]

maybe_fork_scalars() is called for both BPF_AND and BPF_OR when the
source operand is a constant.  When dst has signed range [-1, 0], it
forks the verifier state: the pushed path gets dst = 0, the current
path gets dst = -1.

For BPF_AND this is correct: 0 & K == 0.
For BPF_OR this is wrong:    0 | K == K, not 0.

The pushed path therefore tracks dst as 0 when the runtime value is K,
producing an exploitable verifier/runtime divergence that allows
out-of-bounds map access.

Fix this by passing env->insn_idx (instead of env->insn_idx + 1) to
push_stack(), so the pushed path re-executes the ALU instruction with
dst = 0 and naturally computes the correct result for any opcode.

Fixes: bffacdb80b93 ("bpf: Recognize special arithmetic shift in the verifier")
Signed-off-by: Daniel Wade 
Reviewed-by: Amery Hung 
Acked-by: Eduard Zingerman 
Link: https://lore.kernel.org/r/20260314021521.128361-2-danjwade95@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN

2026-04-02T11:09:25+00:00

[ Upstream commit c77b30bd1dcb61f66c640ff7d2757816210c7cb0 ]

The BPF interpreter's signed 32-bit division and modulo handlers use
the kernel abs() macro on s32 operands. The abs() macro documentation
(include/linux/math.h) explicitly states the result is undefined when
the input is the type minimum. When DST contains S32_MIN (0x80000000),
abs((s32)DST) triggers undefined behavior and returns S32_MIN unchanged
on arm64/x86. This value is then sign-extended to u64 as
0xFFFFFFFF80000000, causing do_div() to compute the wrong result.

The verifier's abstract interpretation (scalar32_min_max_sdiv) computes
the mathematically correct result for range tracking, creating a
verifier/interpreter mismatch that can be exploited for out-of-bounds
map value access.

Introduce abs_s32() which handles S32_MIN correctly by casting to u32
before negating, avoiding signed overflow entirely. Replace all 8
abs((s32)...) call sites in the interpreter's sdiv32/smod32 handlers.

s32 is the only affected case -- the s64 division/modulo handlers do
not use abs().

Fixes: ec0e2da95f72 ("bpf: Support new signed div/mod instructions.")
Acked-by: Yonghong Song 
Acked-by: Mykyta Yatsenko 
Signed-off-by: Jenny Guanni Qu 
Link: https://lore.kernel.org/r/20260311011116.2108005-2-qguanni@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Release module BTF IDR before module unload

2026-04-02T11:09:25+00:00

[ Upstream commit 146bd2a87a65aa407bb17fac70d8d583d19aba06 ]

Gregory reported in [0] that the global_map_resize test when run in
repeatedly ends up failing during program load. This stems from the fact
that BTF reference has not dropped to zero after the previous run's
module is unloaded, and the older module's BTF is still discoverable and
visible. Later, in libbpf, load_module_btfs() will find the ID for this
stale BTF, open its fd, and then it will be used during program load
where later steps taking module reference using btf_try_get_module()
fail since the underlying module for the BTF is gone.

Logically, once a module is unloaded, it's associated BTF artifacts
should become hidden. The BTF object inside the kernel may still remain
alive as long its reference counts are alive, but it should no longer be
discoverable.

To fix this, let us call btf_free_id() from the MODULE_STATE_GOING case
for the module unload to free the BTF associated IDR entry, and disable
its discovery once module unload returns to user space. If a race
happens during unload, the outcome is non-deterministic anyway. However,
user space should be able to rely on the guarantee that once it has
synchronously established a successful module unload, no more stale
artifacts associated with this module can be obtained subsequently.

Note that we must be careful to not invoke btf_free_id() in btf_put()
when btf_is_module() is true now. There could be a window where the
module unload drops a non-terminal reference, frees the IDR, but the
same ID gets reused and the second unconditional btf_free_id() ends up
releasing an unrelated entry.

To avoid a special case for btf_is_module() case, set btf->id to zero to
make btf_free_id() idempotent, such that we can unconditionally invoke it
from btf_put(), and also from the MODULE_STATE_GOING case. Since zero is
an invalid IDR, the idr_remove() should be a noop.

Note that we can be sure that by the time we reach final btf_put() for
btf_is_module() case, the btf_free_id() is already done, since the
module itself holds the BTF reference, and it will call this function
for the BTF before dropping its own reference.

  [0]: https://lore.kernel.org/bpf/cover.1773170190.git.grbell@redhat.com

Fixes: 36e68442d1af ("bpf: Load and verify kernel module BTFs")
Acked-by: Martin KaFai Lau 
Suggested-by: Martin KaFai Lau 
Reported-by: Gregory Bell 
Reviewed-by: Emil Tsalapatis 
Signed-off-by: Kumar Kartikeya Dwivedi 
Link: https://lore.kernel.org/r/20260312205307.1346991-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix constant blinding for PROBE_MEM32 stores

2026-04-02T11:09:24+00:00

[ Upstream commit 2321a9596d2260310267622e0ad8fbfa6f95378f ]

BPF_ST | BPF_PROBE_MEM32 immediate stores are not handled by
bpf_jit_blind_insn(), allowing user-controlled 32-bit immediates to
survive unblinded into JIT-compiled native code when bpf_jit_harden >= 1.

The root cause is that convert_ctx_accesses() rewrites BPF_ST|BPF_MEM
to BPF_ST|BPF_PROBE_MEM32 for arena pointer stores during verification,
before bpf_jit_blind_constants() runs during JIT compilation. The
blinding switch only matches BPF_ST|BPF_MEM (mode 0x60), not
BPF_ST|BPF_PROBE_MEM32 (mode 0xa0). The instruction falls through
unblinded.

Add BPF_ST|BPF_PROBE_MEM32 cases to bpf_jit_blind_insn() alongside the
existing BPF_ST|BPF_MEM cases. The blinding transformation is identical:
load the blinded immediate into BPF_REG_AX via mov+xor, then convert
the immediate store to a register store (BPF_STX).

The rewritten STX instruction must preserve the BPF_PROBE_MEM32 mode so
the architecture JIT emits the correct arena addressing (R12-based on
x86-64). Cannot use the BPF_STX_MEM() macro here because it hardcodes
BPF_MEM mode; construct the instruction directly instead.

Fixes: 6082b6c328b5 ("bpf: Recognize addr_space_cast instruction in the verifier.")
Reviewed-by: Puranjay Mohan 
Reviewed-by: Emil Tsalapatis 
Signed-off-by: Sachin Kumar 
Acked-by: Daniel Borkmann 
Link: https://lore.kernel.org/r/Y6IT5VvNRchPBLI5D7JZHBzZrU9rb0ycRJPJzJSXGj7kJlX8RJwZFSM2YZjcDxoQKABkxt1T8Os2gi23PYyFuQe6KkZGWVyfz8K5afdy9ak=@protonmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim

2026-03-13T16:20:42+00:00

[ Upstream commit 56145d237385ca0e7ca9ff7b226aaf2eb8ef368b ]

The root cause of this bug is that when 'bpf_link_put' reduces the
refcount of 'shim_link->link.link' to zero, the resource is considered
released but may still be referenced via 'tr->progs_hlist' in
'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in
'bpf_shim_tramp_link_release' is deferred. During this window, another
process can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'.

Based on Martin KaFai Lau's suggestions, I have created a simple patch.

To fix this:
   Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'.
   Only increment the refcount if it is not already zero.

Testing:
   I verified the fix by adding a delay in
   'bpf_shim_tramp_link_release' to make the bug easier to trigger:

static void bpf_shim_tramp_link_release(struct bpf_link *link)
{
	/* ... */
	if (!shim_link->trampoline)
		return;

+	msleep(100);
	WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link,
		shim_link->trampoline, NULL));
	bpf_trampoline_put(shim_link->trampoline);
}

Before the patch, running a PoC easily reproduced the crash(almost 100%)
with a call trace similar to KaiyanM's report.
After the patch, the bug no longer occurs even after millions of
iterations.

Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Reported-by: Kaiyan Mei 
Closes: https://lore.kernel.org/bpf/3c4ebb0b.46ff8.19abab8abe2.Coremail.kaiyanm@hust.edu.cn/
Signed-off-by: Lang Xu 
Signed-off-by: Martin KaFai Lau 
Link: https://patch.msgid.link/279EEE1BA1DDB49D+20260303095217.34436-1-xulang@uniontech.com
Signed-off-by: Sasha Levin