5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Xiang Mei <redacted>
[ Upstream commit c7e6b863d298f56522d0d08554bbea7f142e6588 ]
For casefolded encrypted directories ext4 stores an 8-byte hash trailer
after the name (EXT4_DIRENT_HASHES()), at an offset derived from
de->name_len. On the sb_no_casefold_compat_fallback() path ext4_match()
reads that trailer, but ext4_search_dir()'s by-hand pre-check only tests
de->name + de->name_len <= dlimit, which proves the name fits, not the
rounded trailer. A crafted entry whose name ends at the block boundary
passes the check while EXT4_DIRENT_HASHES(de) lands past the block end,
so ext4_match() reads out of bounds on an ordinary lookup. KASAN reports
it as a use-after-free when the page after the directory block holds a
freed object:
BUG: KASAN: use-after-free in ext4_match (fs/ext4/namei.c:1435)
Read of size 4 at addr ffff888010458000 by task exploit
Call Trace:
ext4_match (fs/ext4/namei.c:1435)
ext4_search_dir (fs/ext4/namei.c:1470)
__ext4_find_entry (fs/ext4/namei.c:1268 fs/ext4/namei.c:1632)
ext4_lookup (fs/ext4/namei.c:1703 fs/ext4/namei.c:1769)
...
filename_lookup (fs/namei.c:2842)
vfs_statx (fs/stat.c:353)
__do_sys_newfstatat (fs/stat.c:538)
do_syscall_64 (arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
Require, for hash-in-dirent directories, that the whole entry including
the rounded trailer fits before calling ext4_match(). This is the same
bound ext4_check_dir_entry() already enforces via ext4_dir_rec_len(), so
no well-formed entry is rejected. The other caller, ext4_find_dest_de(),
runs ext4_check_dir_entry() first and is unaffected.
Fixes: 471fbbea7ff7 ("ext4: handle casefolding with encryption")
Reported-by: Weiming Shi <redacted>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <redacted>
Reviewed-by: Andreas Dilger <redacted>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260709184101.441348-1-xmei5@asu.edu (local)
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ext4/namei.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 9327eebace415..2d64d0e3c0e07 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1542,6 +1542,8 @@ int ext4_search_dir(struct buffer_head *bh, char *search_buf, int buf_size,
/* this code is executed quadratically often */
/* do minimal checking `by hand' */
if (de->name + de->name_len <= dlimit &&
+ (!ext4_hash_in_dirent(dir) ||
+ (char *)de + ext4_dir_rec_len(de->name_len, dir) <= dlimit) &&
ext4_match(dir, fname, de)) {
/* found a match - just to be sure, do
* a full check */--
2.53.0