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| author | Jakub Acs <acsjakub@amazon.de> | 2025-10-01 10:09:55 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-10-29 14:08:55 +0100 |
| commit | 3f307a9f7a7a2822e38ac451b73e2244e7279496 (patch) | |
| tree | 7a6b76f28ce13b98f455ae9405a3dafc5e155490 /fs | |
| parent | 7e212cebc863c2c7a82f480446cd731721451691 (diff) | |
| download | linux-3f307a9f7a7a2822e38ac451b73e2244e7279496.tar.gz linux-3f307a9f7a7a2822e38ac451b73e2244e7279496.tar.bz2 linux-3f307a9f7a7a2822e38ac451b73e2244e7279496.zip | |
fs/notify: call exportfs_encode_fid with s_umount
commit a7c4bb43bfdc2b9f06ee9d036028ed13a83df42a upstream.
Calling intotify_show_fdinfo() on fd watching an overlayfs inode, while
the overlayfs is being unmounted, can lead to dereferencing NULL ptr.
This issue was found by syzkaller.
Race Condition Diagram:
Thread 1 Thread 2
-------- --------
generic_shutdown_super()
shrink_dcache_for_umount
sb->s_root = NULL
|
| vfs_read()
| inotify_fdinfo()
| * inode get from mark *
| show_mark_fhandle(m, inode)
| exportfs_encode_fid(inode, ..)
| ovl_encode_fh(inode, ..)
| ovl_check_encode_origin(inode)
| * deref i_sb->s_root *
|
|
v
fsnotify_sb_delete(sb)
Which then leads to:
[ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
[ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
[ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none)
<snip registers, unreliable trace>
[ 32.143353] Call Trace:
[ 32.143732] ovl_encode_fh+0xd5/0x170
[ 32.144031] exportfs_encode_inode_fh+0x12f/0x300
[ 32.144425] show_mark_fhandle+0xbe/0x1f0
[ 32.145805] inotify_fdinfo+0x226/0x2d0
[ 32.146442] inotify_show_fdinfo+0x1c5/0x350
[ 32.147168] seq_show+0x530/0x6f0
[ 32.147449] seq_read_iter+0x503/0x12a0
[ 32.148419] seq_read+0x31f/0x410
[ 32.150714] vfs_read+0x1f0/0x9e0
[ 32.152297] ksys_read+0x125/0x240
IOW ovl_check_encode_origin derefs inode->i_sb->s_root, after it was set
to NULL in the unmount path.
Fix it by protecting calling exportfs_encode_fid() from
show_mark_fhandle() with s_umount lock.
This form of fix was suggested by Amir in [1].
[1]: https://lore.kernel.org/all/CAOQ4uxhbDwhb+2Brs1UdkoF0a3NSdBAOQPNfEHjahrgoKJpLEw@mail.gmail.com/
Fixes: c45beebfde34 ("ovl: support encoding fid from inode with no alias")
Signed-off-by: Jakub Acs <acsjakub@amazon.de>
Cc: Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-unionfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/notify/fdinfo.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c index e933f9c65d90..d2aa8985c055 100644 --- a/fs/notify/fdinfo.c +++ b/fs/notify/fdinfo.c @@ -17,6 +17,7 @@ #include "fanotify/fanotify.h" #include "fdinfo.h" #include "fsnotify.h" +#include "../internal.h" #if defined(CONFIG_PROC_FS) @@ -46,7 +47,12 @@ static void show_mark_fhandle(struct seq_file *m, struct inode *inode) size = f->handle_bytes >> 2; + if (!super_trylock_shared(inode->i_sb)) + return; + ret = exportfs_encode_fid(inode, (struct fid *)f->f_handle, &size); + up_read(&inode->i_sb->s_umount); + if ((ret == FILEID_INVALID) || (ret < 0)) return; |