On 02.07.24 21:44, Richard Weinberger wrote:
> 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>
Reviewed-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
> ---
> 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;
>
--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
