[Qemu-devel] [PATCH 0/3] linux-user: fix corner cases in sendrecvmsg

[Qemu-devel] [PATCH 0/3] linux-user: fix corner cases in sendrecvmsg

[Peter Maydell]

These patches fix some bugs in handling corner cases of
sendrecvmsg; this allows us to pass the LTP 'recvmsg01'
test case.

thanks
-- PMM

Peter Maydell (3):
  linux-user: Fix handling of iovec counts
  linux-user: Fix errno for sendrecvmsg with large iovec length
  linux-user: Allow bad msg_name for recvfrom on connected socket

 linux-user/syscall.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

-- 
1.9.1

[Qemu-devel] [PATCH 1/3] linux-user: Fix handling of iovec counts

[Peter Maydell]

In the kernel the length of an iovec is generally handled as
an unsigned long, not an integer; fix the parameter to
lock_iovec() accordingly.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 linux-user/syscall.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 9dbd711..8d36d6c 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -2647,7 +2647,7 @@ static abi_long do_getsockopt(int sockfd, int level, int optname,
 }
 
 static struct iovec *lock_iovec(int type, abi_ulong target_addr,
-                                int count, int copy)
+                                abi_ulong count, int copy)
 {
     struct target_iovec *target_vec;
     struct iovec *vec;
@@ -2660,7 +2660,7 @@ static struct iovec *lock_iovec(int type, abi_ulong target_addr,
         errno = 0;
         return NULL;
     }
-    if (count < 0 || count > IOV_MAX) {
+    if (count > IOV_MAX) {
         errno = EINVAL;
         return NULL;
     }
@@ -2735,7 +2735,7 @@ static struct iovec *lock_iovec(int type, abi_ulong target_addr,
 }
 
 static void unlock_iovec(struct iovec *vec, abi_ulong target_addr,
-                         int count, int copy)
+                         abi_ulong count, int copy)
 {
     struct target_iovec *target_vec;
     int i;
@@ -2962,7 +2962,7 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
 {
     abi_long ret, len;
     struct msghdr msg;
-    int count;
+    abi_ulong count;
     struct iovec *vec;
     abi_ulong target_vec;
 
-- 
1.9.1

[Qemu-devel] [PATCH 2/3] linux-user: Fix errno for sendrecvmsg with large iovec length

[Peter Maydell]

The sendmsg and recvmsg syscalls use a different errno to indicate
an overlarge iovec length from readv and writev. Handle this
special case in do_sendrcvmsg_locked() to avoid getting the
default errno returned by lock_iovec().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 linux-user/syscall.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 8d36d6c..a21ee59 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -2985,6 +2985,15 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
 
     count = tswapal(msgp->msg_iovlen);
     target_vec = tswapal(msgp->msg_iov);
+
+    if (count > IOV_MAX) {
+        /* sendrcvmsg returns a different errno for this condition than
+         * readv/writev, so we must catch it here before lock_iovec() does.
+         */
+        ret = -TARGET_EMSGSIZE;
+        goto out2;
+    }
+
     vec = lock_iovec(send ? VERIFY_READ : VERIFY_WRITE,
                      target_vec, count, send);
     if (vec == NULL) {
-- 
1.9.1

[Qemu-devel] [PATCH 3/3] linux-user: Allow bad msg_name for recvfrom on connected socket

[Peter Maydell]

The POSIX standard mandates that for a connected socket recvfrom()
must ignore the msg_name and msg_namelen fields. This is awkward
for QEMU because we will attempt to copy them from guest address
space. Handle this by not immediately returning a TARGET_EFAULT
if the copy failed, but instead passing a known-bad address
to the host kernel, which can then return EFAULT or ignore the
value appropriately.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 linux-user/syscall.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index a21ee59..33b5cb6 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -2972,7 +2972,14 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
         ret = target_to_host_sockaddr(fd, msg.msg_name,
                                       tswapal(msgp->msg_name),
                                       msg.msg_namelen);
-        if (ret) {
+        if (ret == -TARGET_EFAULT) {
+            /* For connected sockets msg_name and msg_namelen must
+             * be ignored, so returning EFAULT immediately is wrong.
+             * Instead, pass a bad msg_name to the host kernel, and
+             * let it decide whether to return EFAULT or not.
+             */
+            msg.msg_name = (void *)-1;
+        } else if (ret) {
             goto out2;
         }
     } else {
@@ -3025,7 +3032,7 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
             }
             if (!is_error(ret)) {
                 msgp->msg_namelen = tswap32(msg.msg_namelen);
-                if (msg.msg_name != NULL) {
+                if (msg.msg_name != NULL && msg.msg_name != (void *)-1) {
                     ret = host_to_target_sockaddr(tswapal(msgp->msg_name),
                                     msg.msg_name, msg.msg_namelen);
                     if (ret) {
-- 
1.9.1