Fix unsafe references to errno within error messaging logic.

Various places were supposing that errno could be expected to hold still
within an ereport() nest or similar contexts.  This isn't true necessarily,
though in some cases it accidentally failed to fail depending on how the
compiler chanced to order the subexpressions.  This class of thinko
explains recent reports of odd failures on clang-built versions, typically
missing or inappropriate HINT fields in messages.

Problem identified by Christian Kruse, who also submitted the patch this
commit is based on.  (I fixed a few issues in his patch and found a couple
of additional places with the same disease.)

Back-patch as appropriate to all supported branches.

diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c
index 3cb31baa6926c87738da3b5ac276644ffc3f7721..814039e83adaa5ced769dc967d0420301c40502e 100644 (file)
--- a/src/backend/port/sysv_sema.c
+++ b/src/backend/port/sysv_sema.c
@@ -94,15 +94,17 @@ InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey, int numSems)
 
        if (semId < 0)
        {
+               int                     saved_errno = errno;
+
                /*
                 * Fail quietly if error indicates a collision with existing set. One
                 * would expect EEXIST, given that we said IPC_EXCL, but perhaps we
                 * could get a permission violation instead?  Also, EIDRM might occur
                 * if an old set is slated for destruction but not gone yet.
                 */
-               if (errno == EEXIST || errno == EACCES
+               if (saved_errno == EEXIST || saved_errno == EACCES
 #ifdef EIDRM
-                       || errno == EIDRM
+                       || saved_errno == EIDRM
 #endif
                        )
                        return -1;
@@ -115,7 +117,7 @@ InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey, int numSems)
                                 errdetail("Failed system call was semget(%lu, %d, 0%o).",
                                                   (unsigned long) semKey, numSems,
                                                   IPC_CREAT | IPC_EXCL | IPCProtection),
-                                (errno == ENOSPC) ?
+                                (saved_errno == ENOSPC) ?
                                 errhint("This error does *not* mean that you have run out of disk space.\n"
                  "It occurs when either the system limit for the maximum number of "
                         "semaphore sets (SEMMNI), or the system wide maximum number of "
@@ -141,13 +143,17 @@ IpcSemaphoreInitialize(IpcSemaphoreId semId, int semNum, int value)
 
        semun.val = value;
        if (semctl(semId, semNum, SETVAL, semun) < 0)
+       {
+               int                     saved_errno = errno;
+
                ereport(FATAL,
                                (errmsg_internal("semctl(%d, %d, SETVAL, %d) failed: %m",
                                                                 semId, semNum, value),
-                                (errno == ERANGE) ?
+                                (saved_errno == ERANGE) ?
                                 errhint("You possibly need to raise your kernel's SEMVMX value to be at least "
                                  "%d.  Look into the PostgreSQL documentation for details.",
                                                 value) : 0));
+       }
 }
 
 /*

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index cd81aba0c03e2d5b31ee44beb750d88c6c05b120..98de9346ce4e0fd90b831e40d6ed4c21702ca1e0 100644 (file)
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -79,15 +79,17 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
 
        if (shmid < 0)
        {
+               int                     shmget_errno = errno;
+
                /*
                 * Fail quietly if error indicates a collision with existing segment.
                 * One would expect EEXIST, given that we said IPC_EXCL, but perhaps
                 * we could get a permission violation instead?  Also, EIDRM might
                 * occur if an old seg is slated for destruction but not gone yet.
                 */
-               if (errno == EEXIST || errno == EACCES
+               if (shmget_errno == EEXIST || shmget_errno == EACCES
 #ifdef EIDRM
-                       || errno == EIDRM
+                       || shmget_errno == EIDRM
 #endif
                        )
                        return NULL;
@@ -101,10 +103,8 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
                 * size against SHMMIN in the preexisting-segment case, so we will
                 * not get EINVAL a second time if there is such a segment.
                 */
-               if (errno == EINVAL)
+               if (shmget_errno == EINVAL)
                {
-                       int             save_errno = errno;
-
                        shmid = shmget(memKey, 0, IPC_CREAT | IPC_EXCL | IPCProtection);
 
                        if (shmid < 0)
@@ -130,19 +130,18 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
                                        elog(LOG, "shmctl(%d, %d, 0) failed: %m",
                                                 (int) shmid, IPC_RMID);
                        }
-
-                       errno = save_errno;
                }
 
                /*
                 * Else complain and abort
                 */
+               errno = shmget_errno;
                ereport(FATAL,
                                (errmsg("could not create shared memory segment: %m"),
                  errdetail("Failed system call was shmget(key=%lu, size=%lu, 0%o).",
                                        (unsigned long) memKey, (unsigned long) size,
                                        IPC_CREAT | IPC_EXCL | IPCProtection),
-                                (errno == EINVAL) ?
+                                (shmget_errno == EINVAL) ?
                                 errhint("This error usually means that PostgreSQL's request for a shared memory "
                  "segment exceeded your kernel's SHMMAX parameter.  You can either "
                                                 "reduce the request size or reconfigure the kernel with larger SHMMAX.  "
@@ -155,7 +154,7 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
                "The PostgreSQL documentation contains more information about shared "
                                                 "memory configuration.",
                                                 (unsigned long) size, NBuffers, MaxBackends) : 0,
-                                (errno == ENOMEM) ?
+                                (shmget_errno == ENOMEM) ?
                                 errhint("This error usually means that PostgreSQL's request for a shared "
                                   "memory segment exceeded available memory or swap space. "
                                  "To reduce the request size (currently %lu bytes), reduce "
@@ -164,7 +163,7 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
                "The PostgreSQL documentation contains more information about shared "
                                                 "memory configuration.",
                                                 (unsigned long) size, NBuffers, MaxBackends) : 0,
-                                (errno == ENOSPC) ?
+                                (shmget_errno == ENOSPC) ?
                                 errhint("This error does *not* mean that you have run out of disk space. "
                                                 "It occurs either if all available shared memory IDs have been taken, "
                                                 "in which case you need to raise the SHMMNI parameter in your kernel, "