[PATCH] ext4: prevent out-of-bounds read in ext4_read_inline_data()

[Junjie Cao]

ext4_read_inline_data() reads e_value_offs from the inode buffer_head on
each call, but the decision to enter the xattr value path depends on
i_inline_size cached in EXT4_I(inode) at iget time. If the buffer
contents change after the initial validation, e_value_offs can point
beyond the inode body while i_inline_size still directs the code into
the xattr value path, causing an out-of-bounds read in the memcpy.

Add a bounds check before the memcpy, consistent with
ext4_xattr_ibody_get(). Also guard folio_mark_uptodate() in
ext4_read_inline_folio() since ext4_read_inline_data() can now return
-EFSCORRUPTED.

Fixes: 67cf5b09a46f ("ext4: add the basic function for inline data support")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: syzbot+26c4a8cab92d0cda3e3b@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: syzbot+26c4a8cab92d0cda3e3b@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=26c4a8cab92d0cda3e3b
Signed-off-by: Junjie Cao <junjie.cao@xxxxxxxxx>
---
 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 408677fa8196..18c678df0a6e 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -211,6 +211,14 @@ static int ext4_read_inline_data(struct inode *inode, void *buffer,
 	len = min_t(unsigned int, len,
 		    (unsigned int)le32_to_cpu(entry->e_value_size));
 
+	if (unlikely((void *)IFIRST(header) + le16_to_cpu(entry->e_value_offs) +
+		     len > (void *)ITAIL(inode, raw_inode))) {
+		EXT4_ERROR_INODE(inode,
+			"inline data value out of bounds (offs %u len %u)",
+			le16_to_cpu(entry->e_value_offs), len);
+		return -EFSCORRUPTED;
+	}
+
 	memcpy(buffer,
 	       (void *)IFIRST(header) + le16_to_cpu(entry->e_value_offs), len);
 	cp_len += len;
@@ -535,7 +543,8 @@ static int ext4_read_inline_folio(struct inode *inode, struct folio *folio)
 	ret = ext4_read_inline_data(inode, kaddr, len, &iloc);
 	kaddr = folio_zero_tail(folio, len, kaddr + len);
 	kunmap_local(kaddr);
-	folio_mark_uptodate(folio);
+	if (ret >= 0)
+		folio_mark_uptodate(folio);
 	brelse(iloc.bh);
 
 out:
-- 
2.43.0