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| author | Ahmet Eray Karadag <eraykrdg1@gmail.com> | 2025-09-20 05:13:43 +0300 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2025-09-26 08:36:08 -0400 |
| commit | 57295e835408d8d425bef58da5253465db3d6888 (patch) | |
| tree | d57ce0943e8b847df312980fd70343f7d7159b04 | |
| parent | 04a91570ac67760301e5458d65eaf1342ecca314 (diff) | |
ext4: guard against EA inode refcount underflow in xattr update
syzkaller found a path where ext4_xattr_inode_update_ref() reads an EA
inode refcount that is already <= 0 and then applies ref_change (often
-1). That lets the refcount underflow and we proceed with a bogus value,
triggering errors like:
EXT4-fs error: EA inode <n> ref underflow: ref_count=-1 ref_change=-1
EXT4-fs warning: ea_inode dec ref err=-117
Make the invariant explicit: if the current refcount is non-positive,
treat this as on-disk corruption, emit ext4_error_inode(), and fail the
operation with -EFSCORRUPTED instead of updating the refcount. Delete the
WARN_ONCE() as negative refcounts are now impossible; keep error reporting
in ext4_error_inode().
This prevents the underflow and the follow-on orphan/cleanup churn.
Reported-by: syzbot+0be4f339a8218d2a5bb1@syzkaller.appspotmail.com
Fixes: https://syzbot.org/bug?extid=0be4f339a8218d2a5bb1
Cc: stable@kernel.org
Co-developed-by: Albin Babu Varghese <albinbabuvarghese20@gmail.com>
Signed-off-by: Albin Babu Varghese <albinbabuvarghese20@gmail.com>
Signed-off-by: Ahmet Eray Karadag <eraykrdg1@gmail.com>
Message-ID: <20250920021342.45575-1-eraykrdg1@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
| -rw-r--r-- | fs/ext4/xattr.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 7743d81b2f21..5b680deb1c9b 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -1019,7 +1019,7 @@ static int ext4_xattr_inode_update_ref(handle_t *handle, struct inode *ea_inode, int ref_change) { struct ext4_iloc iloc; - s64 ref_count; + u64 ref_count; int ret; inode_lock_nested(ea_inode, I_MUTEX_XATTR); @@ -1029,13 +1029,17 @@ static int ext4_xattr_inode_update_ref(handle_t *handle, struct inode *ea_inode, goto out; ref_count = ext4_xattr_inode_get_ref(ea_inode); + if ((ref_count == 0 && ref_change < 0) || (ref_count == U64_MAX && ref_change > 0)) { + ext4_error_inode(ea_inode, __func__, __LINE__, 0, + "EA inode %lu ref wraparound: ref_count=%lld ref_change=%d", + ea_inode->i_ino, ref_count, ref_change); + ret = -EFSCORRUPTED; + goto out; + } ref_count += ref_change; ext4_xattr_inode_set_ref(ea_inode, ref_count); if (ref_change > 0) { - WARN_ONCE(ref_count <= 0, "EA inode %lu ref_count=%lld", - ea_inode->i_ino, ref_count); - if (ref_count == 1) { WARN_ONCE(ea_inode->i_nlink, "EA inode %lu i_nlink=%u", ea_inode->i_ino, ea_inode->i_nlink); @@ -1044,9 +1048,6 @@ static int ext4_xattr_inode_update_ref(handle_t *handle, struct inode *ea_inode, ext4_orphan_del(handle, ea_inode); } } else { - WARN_ONCE(ref_count < 0, "EA inode %lu ref_count=%lld", - ea_inode->i_ino, ref_count); - if (ref_count == 0) { WARN_ONCE(ea_inode->i_nlink != 1, "EA inode %lu i_nlink=%u", |