[PATCH] ext4: Fix integer overflow in ext4fs_read_symlink()

While zalloc() takes a size_t type, adding 1 to the le32 variable
will overflow.
A carefully crafted ext4 filesystem can exhibit an inode size of 0xffffffff
and as consequence zalloc() will do a zero allocation.

Later in the function the inode size is again used for copying data.
So an attacker can overwrite memory.

Avoid the overflow by using the __builtin_add_overflow() helper.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-By: Daniel Leidert <dleidert@debian.org>
Origin: https://source.denx.de/u-boot/u-boot/-/commit/35f75d2a46e5859138c83a75cd2f4141c5479ab9
Bug: https://www.openwall.com/lists/oss-security/2025/02/17/2
Bug-Debian: https://bugs.debian.org/1098254
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2024-57256
Bug-Freexian-Security: https://deb.freexian.com/extended-lts/tracker/CVE-2024-57256

Gbp-Pq: Name CVE-2024-57256.patch

diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index c52cc400e1f2c0985234b0ec2352200f1d813d80..6c4f8dcdf823f3b1d273d8817478f362054dca78 100644 (file)
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -2183,13 +2183,17 @@ static char *ext4fs_read_symlink(struct ext2fs_node *node)
        struct ext2fs_node *diro = node;
        int status;
        loff_t actread;
+       size_t alloc_size;
 
        if (!diro->inode_read) {
                status = ext4fs_read_inode(diro->data, diro->ino, &diro->inode);
                if (status == 0)
                        return NULL;
        }
-       symlink = zalloc(le32_to_cpu(diro->inode.size) + 1);
+       if (__builtin_add_overflow(le32_to_cpu(diro->inode.size), 1, &alloc_size))
+               return NULL;
+
+       symlink = zalloc(alloc_size);
        if (!symlink)
                return NULL;