[PATCH 5.10] ext4: fix out-of-bounds read in ext4_read_inline_dir()

[Mikhail Dmitrichenko <mdmitrichenko@astralinux.ru>]

From: Xiang Mei <xmei5@asu.edu>

commit 9333cc809f0a89e001b814155a6cb8903a6274df upstream.

ext4_read_inline_dir() can read a dirent header past the end of its inline
buffer, triggering a slab-out-of-bounds read during getdents64():

  BUG: KASAN: slab-out-of-bounds in __ext4_check_dir_entry
  Read of size 2 at addr ffff88800f3dd23c by task exploit/148
   ...
   __ext4_check_dir_entry
   ext4_read_inline_dir
   iterate_dir

The dirent payload lives in a buffer of exactly inline_size bytes:

	dir_buf = kmalloc(inline_size, GFP_NOFS);

but iteration runs in a position space extra_offset bytes larger
(extra_size = extra_offset + inline_size) so the synthetic "." and ".."
land at their block-dir offsets. A dirent is formed at "dir_buf + pos -
extra_offset", yet the ext4_check_dir_entry() length argument uses the
larger extra_size. A position whose dirent header would extend past
extra_size is therefore accepted, and the rescan loop's rec_len probe and
ext4_check_dir_entry() dereference de->rec_len before the entry is rejected.

Reject a position whose minimum-size dirent header would not fit within
extra_size before forming de, in both the rescan and main loops, and pass
inline_size rather than extra_size to ext4_check_dir_entry() so the length
check matches the physical buffer.

Fixes: c4d8b0235aa9 ("ext4: fix readdir error in case inline_data+^dir_index.")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260615190519.946736-1-xmei5@asu.edu
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[ mdmitrichenko: use EXT4_DIR_REC_LEN(1) instead of
  ext4_dir_rec_len(1, NULL), which does not exist in 5.10; both compute
  the same minimal dirent length. ]
Signed-off-by: Mikhail Dmitrichenko <mdmitrichenko@astralinux.ru>
---
Backport fix for CVE-2026-89786
 fs/ext4/inline.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index edaa88202260..ff96caac04de 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1563,6 +1563,8 @@ int ext4_read_inline_dir(struct file *file,
 			/* for other entry, the real offset in
 			 * the buf has to be tuned accordingly.
 			 */
+			if (i + EXT4_DIR_REC_LEN(1) > extra_size)
+				break;
 			de = (struct ext4_dir_entry_2 *)
 				(dir_buf + i - extra_offset);
 			/* It's too expensive to do a full
@@ -1597,10 +1599,17 @@ int ext4_read_inline_dir(struct file *file,
 			continue;
 		}
 
+		/*
+		 * de lives at dir_buf + ctx->pos - extra_offset, within the
+		 * kmalloc(inline_size) buffer.  Make sure its header fits before
+		 * ext4_check_dir_entry() dereferences de->rec_len.
+		 */
+		if (ctx->pos + EXT4_DIR_REC_LEN(1) > extra_size)
+			goto out;
 		de = (struct ext4_dir_entry_2 *)
 			(dir_buf + ctx->pos - extra_offset);
 		if (ext4_check_dir_entry(inode, file, de, iloc.bh, dir_buf,
-					 extra_size, ctx->pos))
+					 inline_size, ctx->pos))
 			goto out;
 		if (le32_to_cpu(de->inode)) {
 			if (!dir_emit(ctx, de->name, de->name_len,
-- 
2.43.0