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@xxxxxx>
---
I have found and verified this bug in u-boot.
But Barebox uses the same code, so it is most likely affected too.
Thanks,
//richard
---
fs/ext4/ext4_common.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index 4bfb55ad0d..a38593105f 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -369,13 +369,18 @@ char *ext4fs_read_symlink(struct ext2fs_node *node)
char *symlink;
struct ext2fs_node *diro = node;
int status, ret;
+ size_t alloc_size;
if (!diro->inode_read) {
ret = ext4fs_read_inode(diro->data, diro->ino, &diro->inode);
if (ret)
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 0;
--
2.35.3
