netfilter: nf_log: fix uninit read in nf_log_proc_dostring

[ Upstream commit dffd22aed2aa1e804bccf19b30a421e89ee2ae61 ]

When proc_dostring() is called with a non-zero offset in strict mode, it
doesn't just write to the ->data buffer, it also reads. Make sure it
doesn't read uninitialized data.

Fixes: c6ac37d8d884 ("netfilter: nf_log: fix error on write NONE to [...]")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
index 276324abfa604dfcdca6a864daf67958f66b907f..cdc744aa58893cfa80169cc368669ed51805eba3 100644 (file)
--- a/net/netfilter/nf_log.c
+++ b/net/netfilter/nf_log.c
@@ -440,6 +440,10 @@ static int nf_log_proc_dostring(struct ctl_table *table, int write,
        if (write) {
                struct ctl_table tmp = *table;
 
+               /* proc_dostring() can append to existing strings, so we need to
+                * initialize it as an empty string.
+                */
+               buf[0] = '\0';
                tmp.data = buf;
                r = proc_dostring(&tmp, write, buffer, lenp, ppos);
                if (r)