Messages in this thread | | | Subject | Re: [PATCH] kernfs: fix potential null-ptr-deref in kernfs_path_from_node_locked() | From | "Leizhen (ThunderTown)" <> | Date | Thu, 24 Nov 2022 10:28:21 +0800 |
| |
On 2022/11/24 10:24, Leizhen (ThunderTown) wrote: > > > On 2022/11/24 0:55, Tejun Heo wrote: >> On Wed, Nov 23, 2022 at 10:04:19AM +0800, Zhen Lei wrote: >>> Ensure that the 'buf' is not empty before strlcpy() uses it. >>> >>> Commit bbe70e4e4211 ("fs: kernfs: Fix possible null-pointer dereferences >>> in kernfs_path_from_node_locked()") first noticed this, but it didn't >>> fix it completely. >>> >>> Fixes: 9f6df573a404 ("kernfs: Add API to generate relative kernfs path") >>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> >> >> I think the right thing to do is removing that if. It makes no sense to call >> that function with NULL buf and the fact that nobody reported crashes on >> NULL buf indicates that we in fact never do. > > OK. > > How about I remove "buf[0] = '\0';" too? It seems to be a useless operation. > When 'kn_from' and 'kn_to' have a common ancestor, there must be a path from > 'kn_from' to 'kn_to', and strlcpy() always fills in the terminator correctly, > even if the buf is too small to save the first path node.
Sorry, I misanalyzed. The length used by "len < buflen ? buflen - len : 0" may be zero.
> > static void test(void) > { > char buf[4]; > int i, n, buflen; > > buflen = 1; > n = strlcpy(buf, "string", buflen); > for (i = 0; i < buflen; i++) > printk("%d: %02x\n", i, buf[i]); > printk("n=%d\n\n", n); > > buflen = sizeof(buf); > n = strlcpy(buf, "string", buflen); > for (i = 0; i < buflen; i++) > printk("%d: %02x\n", i, buf[i]); > printk("n=%d\n", n); > } > > Output: > [ 33.691497] 0: 00 > [ 33.691569] n=6 > > [ 33.691595] 0: 73 > [ 33.691622] 1: 74 > [ 33.691630] 2: 72 > [ 33.691637] 3: 00 > [ 33.691650] n=6 > >> >> Thanks. >> >
-- Regards, Zhen Lei
| |