Previously, when writing to /proc/net/rpc/*/channel, if a cache line
were larger than the default buffer size (likely 1024 bytes), mountd
and svcgssd would split writes into a number of buffer-sized writes.
Each of these writes would get an EINVAL error back from the kernel
procfs handle (it expects line-oriented input and does not account for
multiple/split writes), and no cache update would occur.
When such behavior occurs, NFS clients depending on mountd to finish
the cache operation would block/hang, or receive EPERM, depending on
the context of the operation. This is likely to happen if a user is a
member of a large (~100-200) number of groups.
Instead, every fopen() on the procfs files in question is followed by
a call to setvbuf(), using a per-file dedicated buffer of
RPC_CHAN_BUF_SIZE length.
Really, mountd should not be using stdio-style buffered file operations
on files in /proc to begin with. A better solution would be to use
internally managed buffers and calls to write() instead of these stdio
calls, but that would be a more extensive change; so this is proposed
as a quick and not-so-dirty fix in the meantime.
Signed-off-by: Sean Finney <sean.finney@xxxxxxxxxxxxxxxx>
---
support/include/misc.h | 3 +++
utils/gssd/svcgssd_proc.c | 3 +++
utils/mountd/cache.c | 2 ++
3 files changed, 8 insertions(+), 0 deletions(-)
diff --git a/support/include/misc.h b/support/include/misc.h
index 9a1b25d..7e3874e 100644
--- a/support/include/misc.h
+++ b/support/include/misc.h
@@ -24,4 +24,7 @@ struct hostent *get_reliable_hostbyaddr(const char *addr, int len, int type);
extern int is_mountpoint(char *path);
+/* size of the file pointer buffers for rpc procfs files */
+#define RPC_CHAN_BUF_SIZE 32768
+
#endif /* MISC_H */
diff --git a/utils/gssd/svcgssd_proc.c b/utils/gssd/svcgssd_proc.c
index 6f2ba61..8f6548e 100644
--- a/utils/gssd/svcgssd_proc.c
+++ b/utils/gssd/svcgssd_proc.c
@@ -56,6 +56,7 @@
#include "gss_util.h"
#include "err_util.h"
#include "context.h"
+#include "misc.h"
extern char * mech2file(gss_OID mech);
#define SVCGSSD_CONTEXT_CHANNEL "/proc/net/rpc/auth.rpcsec.context/channel"
@@ -78,6 +79,7 @@ do_svc_downcall(gss_buffer_desc *out_handle, struct svc_cred *cred,
FILE *f;
int i;
char *fname = NULL;
+ char vbuf[RPC_CHAN_BUF_SIZE];
int err;
printerr(1, "doing downcall\n");
@@ -90,6 +92,7 @@ do_svc_downcall(gss_buffer_desc *out_handle, struct svc_cred *cred,
SVCGSSD_CONTEXT_CHANNEL, strerror(errno));
goto out_err;
}
+ setvbuf(f, vbuf, _IOLBF, RPC_CHAN_BUF_SIZE);
qword_printhex(f, out_handle->value, out_handle->length);
/* XXX are types OK for the rest of this? */
/* For context cache, use the actual context endtime */
diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
index 34808cd..bd67157 100644
--- a/utils/mountd/cache.c
+++ b/utils/mountd/cache.c
@@ -739,6 +739,7 @@ struct {
char *cache_name;
void (*cache_handle)(FILE *f);
FILE *f;
+ char vbuf[RPC_CHAN_BUF_SIZE];
} cachelist[] = {
{ "auth.unix.ip", auth_unix_ip},
{ "auth.unix.gid", auth_unix_gid},
@@ -757,6 +758,7 @@ void cache_open(void)
continue;
sprintf(path, "/proc/net/rpc/%s/channel", cachelist[i].cache_name);
cachelist[i].f = fopen(path, "r+");
+ setvbuf(cachelist[i].f, cachelist[i].vbuf, _IOLBF, RPC_CHAN_BUF_SIZE);
}
}
--
1.7.4.1
--
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