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 10:24:21 +0800 |
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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.
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
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