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/commands/tablespace.c b/src/backend/commands/tablespace.c
index 22b489a9204984e23d54e429d24521f8f013d9f1..c80821e2d57ee8fcb53da7a8ca616b934ec0b297 100644 (file)
--- a/src/backend/commands/tablespace.c
+++ b/src/backend/commands/tablespace.c
@@ -769,10 +769,14 @@ remove_symlink:
        else
        {
                if (unlink(linkloc) < 0)
-                       ereport(redo ? LOG : (errno == ENOENT ? WARNING : ERROR),
+               {
+                       int                     saved_errno = errno;
+
+                       ereport(redo ? LOG : (saved_errno == ENOENT ? WARNING : ERROR),
                                        (errcode_for_file_access(),
                                         errmsg("could not remove symbolic link \"%s\": %m",
                                                        linkloc)));
+               }
        }
 
        pfree(linkloc_with_version_dir);

diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c
index 2bc4b496116c3ac8e3874e3aa2bcfd28244a2163..7b671869267fb27cc79c71e000c7153ee4d76cf1 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.  "
                  "It occurs when either the system limit for the maximum number of "
                         "semaphore sets (SEMMNI), or the system wide maximum number of "
@@ -139,13 +141,17 @@ 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 285d5f20ae5f6109764896c38a6479281cba518c..3840ad7b1b2974b5aada6648566626ec7e2f69e1 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)
                 * 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)
@@ -130,8 +130,6 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
                                        elog(LOG, "shmctl(%d, %d, 0) failed: %m",
                                                 (int) shmid, IPC_RMID);
                        }
-
-                       errno = save_errno;
                }
 
                /*
@@ -143,12 +141,13 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
                 * it should be.  SHMMNI violation is ENOSPC, per spec.  Just plain
                 * not-enough-RAM is ENOMEM.
                 */
+               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.  "
@@ -161,7 +160,7 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
                "The PostgreSQL documentation contains more information about shared "
                                                 "memory configuration.",
                                                 (unsigned long) size) : 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, "
                           "or exceeded your kernel's SHMALL parameter.  You can either "
@@ -172,7 +171,7 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
                "The PostgreSQL documentation contains more information about shared "
                                                 "memory configuration.",
                                                 (unsigned long) size) : 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, "