The patch titled
Subject: Squashfs: sanity check symbolic link size
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
squashfs-sanity-check-symbolic-link-size.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/squashfs-sanity-check-symbolic-link-size.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
Subject: Squashfs: sanity check symbolic link size
Date: Sun, 11 Aug 2024 21:13:01 +0100
Syzkiller reports a "KMSAN: uninit-value in pick_link" bug.
This is caused by an uninitialised page, which is ultimately caused
by a corrupted symbolic link size read from disk.
The reason why the corrupted symlink size causes an uninitialised
page is due to the following sequence of events:
1. squashfs_read_inode() is called to read the symbolic
link from disk. This assigns the corrupted value
3875536935 to inode->i_size.
2. Later squashfs_symlink_read_folio() is called, which assigns
this corrupted value to the length variable, which being a
signed int, overflows producing a negative number.
3. The following loop that fills in the page contents checks that
the copied bytes is less than length, which being negative means
the loop is skipped, producing an unitialised page.
This patch adds a sanity check which checks that the symbolic
link size is not larger than expected.
Link: https://lkml.kernel.org/r/20240811201301.13076-1-phillip@xxxxxxxxxxxxxxx
Signed-off-by: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
Reported-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
Reported-by: syzbot+24ac24ff58dc5b0d26b9@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/all/000000000000a90e8c061e86a76b@xxxxxxxxxx/
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/squashfs/inode.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/fs/squashfs/inode.c~squashfs-sanity-check-symbolic-link-size
+++ a/fs/squashfs/inode.c
@@ -279,8 +279,13 @@ int squashfs_read_inode(struct inode *in
if (err < 0)
goto failed_read;
- set_nlink(inode, le32_to_cpu(sqsh_ino->nlink));
inode->i_size = le32_to_cpu(sqsh_ino->symlink_size);
+ if (inode->i_size > PAGE_SIZE) {
+ ERROR("Corrupted symlink\n");
+ return -EINVAL;
+ }
+
+ set_nlink(inode, le32_to_cpu(sqsh_ino->nlink));
inode->i_op = &squashfs_symlink_inode_ops;
inode_nohighmem(inode);
inode->i_data.a_ops = &squashfs_symlink_aops;
_
Patches currently in -mm which might be from phillip@xxxxxxxxxxxxxxx are
squashfs-sanity-check-symbolic-link-size.patch
