linux-kernel - [PATCH] Squashfs: reject negative file sizes in squashfs_read

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Message-Id: <20250926215935.107233-1-phillip@squashfs.org.uk>
Date: Fri, 26 Sep 2025 22:59:35 +0100
From: Phillip Lougher <phillip@...ashfs.org.uk>
To: akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Cc: amir73il@...il.com,
	Phillip Lougher <phillip@...ashfs.org.uk>,
	syzbot+f754e01116421e9754b9@...kaller.appspotmail.com
Subject: [PATCH] Squashfs: reject negative file sizes in squashfs_read_inode()

Syskaller reports a "WARNING in ovl_copy_up_file" in overlayfs.

This warning is ultimately caused because the underlying
Squashfs file system returns a file with a negative file size.

This commit checks for a negative file size and returns EINVAL.

Fixes: 6545b246a2c8 ("Squashfs: inode operations")
Reported-by: syzbot+f754e01116421e9754b9@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/68d580e5.a00a0220.303701.0019.GAE@google.com/

Signed-off-by: Phillip Lougher <phillip@...ashfs.org.uk>
---
 fs/squashfs/inode.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/fs/squashfs/inode.c b/fs/squashfs/inode.c
index 5920a33e44a1..8bbdd74a8d29 100644
--- a/fs/squashfs/inode.c
+++ b/fs/squashfs/inode.c
@@ -141,6 +141,10 @@ int squashfs_read_inode(struct inode *inode, long long ino)
 			goto failed_read;
 
 		inode->i_size = le32_to_cpu(sqsh_ino->file_size);
+		if (inode->i_size < 0) {
+			err = -EINVAL;
+			goto failed_read;
+		}
 		frag = le32_to_cpu(sqsh_ino->fragment);
 		if (frag != SQUASHFS_INVALID_FRAG) {
 			/*
@@ -192,6 +196,10 @@ int squashfs_read_inode(struct inode *inode, long long ino)
 			goto failed_read;
 
 		inode->i_size = le64_to_cpu(sqsh_ino->file_size);
+		if (inode->i_size < 0) {
+			err = -EINVAL;
+			goto failed_read;
+		}
 		frag = le32_to_cpu(sqsh_ino->fragment);
 		if (frag != SQUASHFS_INVALID_FRAG) {
 			/*
@@ -243,8 +251,12 @@ int squashfs_read_inode(struct inode *inode, long long ino)
 		if (err < 0)
 			goto failed_read;
 
-		set_nlink(inode, le32_to_cpu(sqsh_ino->nlink));
 		inode->i_size = le16_to_cpu(sqsh_ino->file_size);
+		if (inode->i_size < 0) {
+			err = -EINVAL;
+			goto failed_read;
+		}
+		set_nlink(inode, le32_to_cpu(sqsh_ino->nlink));
 		inode->i_op = &squashfs_dir_inode_ops;
 		inode->i_fop = &squashfs_dir_ops;
 		inode->i_mode |= S_IFDIR;
@@ -267,9 +279,13 @@ int squashfs_read_inode(struct inode *inode, long long ino)
 		if (err < 0)
 			goto failed_read;
 
+		inode->i_size = le32_to_cpu(sqsh_ino->file_size);
+		if (inode->i_size < 0) {
+			err = -EINVAL;
+			goto failed_read;
+		}
 		xattr_id = le32_to_cpu(sqsh_ino->xattr);
 		set_nlink(inode, le32_to_cpu(sqsh_ino->nlink));
-		inode->i_size = le32_to_cpu(sqsh_ino->file_size);
 		inode->i_op = &squashfs_dir_inode_ops;
 		inode->i_fop = &squashfs_dir_ops;
 		inode->i_mode |= S_IFDIR;
@@ -296,7 +312,7 @@ int squashfs_read_inode(struct inode *inode, long long ino)
 			goto failed_read;
 
 		inode->i_size = le32_to_cpu(sqsh_ino->symlink_size);
-		if (inode->i_size > PAGE_SIZE) {
+		if (inode->i_size < 0 || inode->i_size > PAGE_SIZE) {
 			ERROR("Corrupted symlink\n");
 			return -EINVAL;
 		}
-- 
2.39.2