On 12-10-2020 13:29, Dominique Martinet wrote:

Anant Thazhemadam wrote on Mon, Oct 12, 2020:

quoted

In p9_fd_create_unix, checking is performed to see if the addr (passed
as an argument) is NULL or not.
However, no check is performed to see if addr is a valid address, i.e.,
it doesn't entirely consist of only 0's.
The initialization of sun_server.sun_path to be equal to this faulty
addr value leads to an uninitialized variable, as detected by KMSAN.
Checking for this (faulty addr) and returning a negative error number
appropriately, resolves this issue.

I'm not sure I agree a fully zeroed address is faulty but I agree we can
probably refuse it given userspace can't pass useful abstract addresses
here.

Understood. It's  probably a better that I modify the commit message a little and
send a v2 so it becomes more accurate.

Just one nitpick but this is otherwise fine - good catch!

Thank you!

quoted

Reported-by: syzbot+75d51fe5bf4ebe988518@syzkaller.appspotmail.com
Tested-by: syzbot+75d51fe5bf4ebe988518@syzkaller.appspotmail.com
Signed-off-by: Anant Thazhemadam <redacted>
---
 net/9p/trans_fd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index c0762a302162..8f528e783a6c 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c

@@ -1023,7 +1023,7 @@ p9_fd_create_unix(struct p9_client *client, const char *addr, char *args)
 
 	csocket = NULL;
 
-	if (addr == NULL)
+	if (!addr || !strlen(addr))

Since we don't care about the actual length here, how about checking for
addr[0] directly?
That'll spare a strlen() call in the valid case.

You mentioned how a fully zeroed address isn't exactly faulty. By extension, wouldn't that
mean that an address that simply begins with a 0 isn't faulty as well?
This is an interesting point, because if the condition is modified to checking for addr[0] directly,
addresses that simply begin with 0 (but have more non-zero content following) wouldn't be
copied over either, right?
In the end, it comes down to what you define as a "valid" value that sun_path can have.
We've already agreed that a fully zeroed address wouldn't qualify as a valid value for sun_path.
Are addresses that aren't fully zeroed, but only begin with a 0 also to be considered as an
unacceptable value for sun_path?

Thanks,
Anant




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