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netlink-socket: ignore ECHRNG/EXFULL errors from recvmsg_safe() if we expect truncation

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When we receive a netlink messages from userspace we need to drop it
from the queue. Hence we need call recvmsg() on the socket for it. We do
this with a zero-size socket read() buffer, so that the message would be
truncated when copied to userspace, and we do not have to allocate any
memory for it, but it's still dropped.

This was broken in ad501930d7, which
turned datagram truncation into an error (rightfully so I think – for
the common case). That broke this code here, because here we *expect*
truncation, and need to handle it gracefully.

Hence simply check for the two error codes for truncated payload or
cdata, and eat it up.
This commit is contained in:
Lennart Poettering
2025-04-17 08:26:06 +02:00
parent 6d88e4a4b4
commit 90755dac69
1 changed files with 13 additions and 10 deletions
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src/libsystemd/sd-netlink/netlink-socket.c
+13 -10
View File
@@ -162,11 +162,8 @@ static int socket_recv_message(int fd, void *buf, size_t buf_size, uint32_t *ret
assert(peek || (buf && buf_size > 0));
n = recvmsg_safe(fd, &msg, peek ? (MSG_PEEK|MSG_TRUNC) : 0);
if (ERRNO_IS_NEG_TRANSIENT(n)) {
if (ret_mcast_group)
*ret_mcast_group = 0;
return 0;
}
if (ERRNO_IS_NEG_TRANSIENT(n))
goto transient;
if (n == -ENOBUFS)
return log_debug_errno(n, "sd-netlink: kernel receive buffer overrun");
if (n == -ECHRNG)
@@ -181,15 +178,15 @@ static int socket_recv_message(int fd, void *buf, size_t buf_size, uint32_t *ret
log_debug("sd-netlink: ignoring message from PID %"PRIu32, sender.nl.nl_pid);
if (peek) {
/* drop the message */
/* Drop the message. Note that we ignore ECHRNG/EXFULL errors here, which
* recvmsg_safe() returns in case the payload or cdata is truncated. Here it's quite
* likely it is truncated, because we pass a zero-sized buffer. */
n = recvmsg_safe(fd, &msg, 0);
if (n < 0)
if (n < 0 && !IN_SET(n, -ECHRNG, -EXFULL))
return (int) n;
}
if (ret_mcast_group)
*ret_mcast_group = 0;
return 0;
goto transient;
}
if (ret_mcast_group) {
@@ -203,6 +200,12 @@ static int socket_recv_message(int fd, void *buf, size_t buf_size, uint32_t *ret
}
return (int) n;
transient:
if (ret_mcast_group)
*ret_mcast_group = 0;
return 0;
}
DEFINE_PRIVATE_HASH_OPS_WITH_VALUE_DESTRUCTOR(