Fix race condition in pg_ctl reading postmaster.pid.

If postmaster changed postmaster.pid while pg_ctl was reading it, pg_ctl
could overrun the buffer it allocated for the file. Fix by reading the
whole file to memory with one read() call.

initdb contains an identical copy of the readfile() function, but the files
that initdb reads are static, not modified concurrently. Nevertheless, add
a simple bounds-check there, if only to silence static analysis tools.

Per report from Dave Vitek. Backpatch to all supported branches.

diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index c56f721e08f613840b3ff438be9c21542432d9d3..0aa1e800d4808e15ccee097a269e14c361132b0e 100644 (file)
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -417,6 +417,7 @@ readfile(const char *path)
    int         maxlength = 1,
                linelen = 0;
    int         nlines = 0;
+   int         n;
    char      **result;
    char       *buffer;
    int         c;
@@ -454,13 +455,13 @@ readfile(const char *path)
 
    /* now reprocess the file and store the lines */
    rewind(infile);
-   nlines = 0;
-   while (fgets(buffer, maxlength + 1, infile) != NULL)
-       result[nlines++] = pg_strdup(buffer);
+   n = 0;
+   while (fgets(buffer, maxlength + 1, infile) != NULL && n < nlines)
+       result[n++] = pg_strdup(buffer);
 
    fclose(infile);
    free(buffer);
-   result[nlines] = NULL;
+   result[n] = NULL;
 
    return result;
 }

diff --git a/src/bin/pg_ctl/pg_ctl.c b/src/bin/pg_ctl/pg_ctl.c
index 23c47f62752bc54bb0182d4f948588a2e1d7d25a..d550d6f1b4bd64229cb300f0e0266efe1a80039d 100644 (file)
--- a/src/bin/pg_ctl/pg_ctl.c
+++ b/src/bin/pg_ctl/pg_ctl.c
@@ -20,6 +20,7 @@
 #include "postgres_fe.h"
 #include "libpq-fe.h"
 
+#include <fcntl.h>
 #include <locale.h>
 #include <signal.h>
 #include <time.h>
@@ -315,50 +316,77 @@ get_pgpid(void)
 static char **
 readfile(const char *path)
 {
-   FILE       *infile;
-   int         maxlength = 1,
-               linelen = 0;
-   int         nlines = 0;
+   int         fd;
+   int         nlines;
    char      **result;
    char       *buffer;
-   int         c;
+   char       *linebegin;
+   int         i;
+   int         n;
+   int         len;
+   struct stat statbuf;
 
-   if ((infile = fopen(path, "r")) == NULL)
+   /*
+    * Slurp the file into memory.
+    *
+    * The file can change concurrently, so we read the whole file into memory
+    * with a single read() call. That's not guaranteed to get an atomic
+    * snapshot, but in practice, for a small file, it's close enough for the
+    * current use.
+    */
+   fd = open(path, O_RDONLY | PG_BINARY, 0);
+   if (fd < 0)
        return NULL;
+   if (fstat(fd, &statbuf) < 0)
+       return NULL;
+   if (statbuf.st_size == 0)
+   {
+       /* empty file */
+       result = (char **) pg_malloc(sizeof(char *));
+       *result = NULL;
+       return result;
+   }
+   buffer = pg_malloc(statbuf.st_size + 1);
 
-   /* pass over the file twice - the first time to size the result */
+   len = read(fd, buffer, statbuf.st_size + 1);
+   close(fd);
+   if (len != statbuf.st_size)
+   {
+       /* oops, the file size changed between fstat and read */
+       free(buffer);
+       return NULL;
+   }
 
-   while ((c = fgetc(infile)) != EOF)
+   /* count newlines */
+   nlines = 0;
+   for (i = 0; i < len - 1; i++)
    {
-       linelen++;
-       if (c == '\n')
-       {
+       if (buffer[i] == '\n')
            nlines++;
-           if (linelen > maxlength)
-               maxlength = linelen;
-           linelen = 0;
-       }
    }
+   nlines++; /* account for the last line */
 
-   /* handle last line without a terminating newline (yuck) */
-   if (linelen)
-       nlines++;
-   if (linelen > maxlength)
-       maxlength = linelen;
-
-   /* set up the result and the line buffer */
+   /* set up the result buffer */
    result = (char **) pg_malloc((nlines + 1) * sizeof(char *));
-   buffer = (char *) pg_malloc(maxlength + 1);
 
-   /* now reprocess the file and store the lines */
-   rewind(infile);
-   nlines = 0;
-   while (fgets(buffer, maxlength + 1, infile) != NULL)
-       result[nlines++] = pg_strdup(buffer);
+   /* now split the buffer into lines */
+   linebegin = buffer;
+   n = 0;
+   for (i = 0; i < len; i++)
+   {
+       if (buffer[i] == '\n' || i == len - 1)
+       {
+           int     slen = &buffer[i] - linebegin + 1;
+           char   *linebuf = pg_malloc(slen + 1);
+           memcpy(linebuf, linebegin, slen);
+           linebuf[slen] = '\0';
+           result[n++] = linebuf;
+           linebegin = &buffer[i + 1];
+       }
+   }
+   result[n] = NULL;
 
-   fclose(infile);
    free(buffer);
-   result[nlines] = NULL;
 
    return result;
 }