5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ahmet Eray Karadag eraykrdg1@gmail.com
commit 57295e835408d8d425bef58da5253465db3d6888 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ext4/xattr.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)
--- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -987,7 +987,7 @@ static int ext4_xattr_inode_update_ref(h int ref_change) { struct ext4_iloc iloc; - s64 ref_count; + u64 ref_count; int ret;
inode_lock_nested(ea_inode, I_MUTEX_XATTR); @@ -997,13 +997,17 @@ static int ext4_xattr_inode_update_ref(h 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); @@ -1012,9 +1016,6 @@ static int ext4_xattr_inode_update_ref(h 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",