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>
diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index 7cf0160..76f7102 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -2181,13 +2181,18 @@
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;