util: try to set with SO_{RCV,SND}BUFFORCE when requested size is larger than the kernel limit

The commit 10ce2e0681ac16e7bb3619b7bb1a72a6f98a2f2c inverts the order of
SO_{RCV,SND}BUFFORCE and SO_{RCV,SND}BUF. However, setting buffer size with
SO_{RCV,SND}BUF does not fail even if the requested size is larger than
the kernel limit. Hence, SO_{RCV,SND}BUFFORCE will not use anymore and
the buffer size is always limited by the kernel limit even if we have
the priviledge to ignore the limit.

This makes the buffer size is checked after configuring it with
SO_{RCV,SND}BUF, and if it is still not sufficient, then try to set it
with FORCE command. With this commit, if we have enough priviledge, the
requested buffer size is correctly set.

Hopefully fixes #14417.

(cherry picked from commit b92f350789e33942be0cf85af22a580c1fd483d6)
(cherry picked from commit 4dcae666889ae9469e4406c0bcaffadbc01c4f66)

1 files changed, 28 insertions, 12 deletions

diff --git a/src/basic/socket-util.c b/src/basic/socket-util.c
index 4c12888381..f54b8b4275 100644
--- a/src/basic/socket-util.c
+++ b/src/basic/socket-util.c
@@ -627,13 +627,21 @@ int fd_inc_sndbuf(int fd, size_t n) {
         if (r >= 0 && l == sizeof(value) && (size_t) value >= n*2)
                 return 0;
 
-        /* If we have the privileges we will ignore the kernel limit. */
+        /* First, try to set the buffer size with SO_SNDBUF. */
+        r = setsockopt_int(fd, SOL_SOCKET, SO_SNDBUF, n);
+        if (r < 0)
+                return r;
 
-        if (setsockopt_int(fd, SOL_SOCKET, SO_SNDBUF, n) < 0) {
-                r = setsockopt_int(fd, SOL_SOCKET, SO_SNDBUFFORCE, n);
-                if (r < 0)
-                        return r;
-        }
+        /* SO_SNDBUF above may set to the kernel limit, instead of the requested size.
+         * So, we need to check the actual buffer size here. */
+        r = getsockopt(fd, SOL_SOCKET, SO_SNDBUF, &value, &l);
+        if (r >= 0 && l == sizeof(value) && (size_t) value >= n*2)
+                return 1;
+
+        /* If we have the privileges we will ignore the kernel limit. */
+        r = setsockopt_int(fd, SOL_SOCKET, SO_SNDBUFFORCE, n);
+        if (r < 0)
+                return r;
 
         return 1;
 }
@@ -649,13 +657,21 @@ int fd_inc_rcvbuf(int fd, size_t n) {
         if (r >= 0 && l == sizeof(value) && (size_t) value >= n*2)
                 return 0;
 
-        /* If we have the privileges we will ignore the kernel limit. */
+        /* First, try to set the buffer size with SO_RCVBUF. */
+        r = setsockopt_int(fd, SOL_SOCKET, SO_RCVBUF, n);
+        if (r < 0)
+                return r;
 
-        if (setsockopt_int(fd, SOL_SOCKET, SO_RCVBUF, n) < 0) {
-                r = setsockopt_int(fd, SOL_SOCKET, SO_RCVBUFFORCE, n);
-                if (r < 0)
-                        return r;
-        }
+        /* SO_RCVBUF above may set to the kernel limit, instead of the requested size.
+         * So, we need to check the actual buffer size here. */
+        r = getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &value, &l);
+        if (r >= 0 && l == sizeof(value) && (size_t) value >= n*2)
+                return 1;
+
+        /* If we have the privileges we will ignore the kernel limit. */
+        r = setsockopt_int(fd, SOL_SOCKET, SO_RCVBUFFORCE, n);
+        if (r < 0)
+                return r;
 
         return 1;
 }