[PATCH 6.19 299/342] ext4: validate p_idx bounds in ext4_ext_correct_indexes

Greg Kroah-Hartman
2026-03-31T16:44:12Z

From: Tejas Bharambe <tejas.bharambe@outlook.com>

commit 2acb5c12ebd860f30e4faf67e6cc8c44ddfe5fe8 upstream.

ext4_ext_correct_indexes() walks up the extent tree correcting
index entries when the first extent in a leaf is modified. Before
accessing path[k].p_idx->ei_block, there is no validation that
p_idx falls within the valid range of index entries for that
level.

If the on-disk extent header contains a corrupted or crafted
eh_entries value, p_idx can point past the end of the allocated
buffer, causing a slab-out-of-bounds read.

Fix this by validating path[k].p_idx against EXT_LAST_INDEX() at
both access sites: before the while loop and inside it. Return
-EFSCORRUPTED if the index pointer is out of range, consistent
with how other bounds violations are handled in the ext4 extent
tree code.

Reported-by: syzbot+04c4e65cab786a2e5b7e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=04c4e65cab786a2e5b7e
Signed-off-by: Tejas Bharambe <tejas.bharambe@outlook.com>
Link: https://patch.msgid.link/JH0PR06MB66326016F9B6AD24097D232B897CA@JH0PR06MB6632.apcprd06.prod.outlook.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/extents.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1741,6 +1741,13 @@ static int ext4_ext_correct_indexes(hand
err = ext4_ext_get_access(handle, inode, path + k);
if (err)
return err;
+ if (unlikely(path[k].p_idx > EXT_LAST_INDEX(path[k].p_hdr))) {
+ EXT4_ERROR_INODE(inode,
+ "path[%d].p_idx %p > EXT_LAST_INDEX %p",
+ k, path[k].p_idx,
+ EXT_LAST_INDEX(path[k].p_hdr));
+ return -EFSCORRUPTED;
+ }
path[k].p_idx->ei_block = border;
err = ext4_ext_dirty(handle, inode, path + k);
if (err)
@@ -1753,6 +1760,14 @@ static int ext4_ext_correct_indexes(hand
err = ext4_ext_get_access(handle, inode, path + k);
if (err)
goto clean;
+ if (unlikely(path[k].p_idx > EXT_LAST_INDEX(path[k].p_hdr))) {
+ EXT4_ERROR_INODE(inode,
+ "path[%d].p_idx %p > EXT_LAST_INDEX %p",
+ k, path[k].p_idx,
+ EXT_LAST_INDEX(path[k].p_hdr));
+ err = -EFSCORRUPTED;
+ goto clean;
+ }
path[k].p_idx->ei_block = border;
err = ext4_ext_dirty(handle, inode, path + k);
if (err)