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ext4: fix out-of-bounds read in ext4_read_inline_dir()

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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: c4d8b0235a ("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>
This commit is contained in:
Xiang Mei 2026-06-15 12:05:19 -07:00 committed by Theodore Ts'o
parent 7f0485dd30
commit 9333cc809f
1 changed files with 10 additions and 1 deletions
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11
fs/ext4/inline.c
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@ -1454,6 +1454,8 @@ 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, NULL) > extra_size)
break;
de = (struct ext4_dir_entry_2 *)
(dir_buf + i - extra_offset);
/* It's too expensive to do a full
@ -1488,10 +1490,17 @@ 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, NULL) > 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,