Avoid using unsafe C functions (#10932)

replace use of:
sprintf --> snprintf
strcpy/strncpy  --> redis_strlcpy
strcat/strncat  --> redis_strlcat

**why are we making this change?**
Much of the code uses some unsafe variants or deprecated buffer handling
functions.
While most cases are probably not presenting any issue on the known path
programming errors and unterminated strings might lead to potential
buffer overflows which are not covered by tests.

**As part of this PR we change**
1. added implementation for redis_strlcpy and redis_strlcat based on the strl implementation: https://linux.die.net/man/3/strl
2. change all occurrences of use of sprintf with use of snprintf
3. change occurrences of use of  strcpy/strncpy with redis_strlcpy
4. change occurrences of use of strcat/strncat with redis_strlcat
5. change the behavior of ll2string/ull2string/ld2string so that it will always place null
  termination ('\0') on the output buffer in the first index. this was done in order to make
  the use of these functions more safe in cases were the user will not check the output
  returned by them (for example in rdbRemoveTempFile)
6. we added a compiler directive to issue a deprecation error in case a use of
  sprintf/strcpy/strcat is found during compilation which will result in error during compile time.
  However keep in mind that since the deprecation attribute is not supported on all compilers,
  this is expected to fail during push workflows.


**NOTE:** while this is only an initial milestone. We might also consider
using the *_s implementation provided by the C11 Extensions (however not
yet widly supported). I would also suggest to start
looking at static code analyzers to track unsafe use cases.
For example LLVM clang checker supports security.insecureAPI.DeprecatedOrUnsafeBufferHandling
which can help locate unsafe function usage.
https://clang.llvm.org/docs/analyzer/checkers.html#security-insecureapi-deprecatedorunsafebufferhandling-c
The main reason not to onboard it at this stage is that the alternative
excepted by clang is to use the C11 extensions which are not always
supported by stdlib.

1 files changed, 86 insertions, 0 deletions

diff --git a/src/strl.c b/src/strl.c
new file mode 100644
index 000000000..f73cf796c
--- /dev/null
+++ b/src/strl.c
@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 1998, 2015 Todd C. Miller <millert@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include <string.h>
+
+/*
+ * Copy string src to buffer dst of size dsize.  At most dsize-1
+ * chars will be copied.  Always NUL terminates (unless dsize == 0).
+ * Returns strlen(src); if retval >= dsize, truncation occurred.
+ */
+size_t
+redis_strlcpy(char *dst, const char *src, size_t dsize)
+{
+    const char *osrc = src;
+    size_t nleft = dsize;
+
+    /* Copy as many bytes as will fit. */
+    if (nleft != 0) {
+        while (--nleft != 0) {
+            if ((*dst++ = *src++) == '\0')
+                break;
+        }
+    }
+
+    /* Not enough room in dst, add NUL and traverse rest of src. */
+    if (nleft == 0) {
+        if (dsize != 0)
+            *dst = '\0';        /* NUL-terminate dst */
+        while (*src++)
+            ;
+    }
+
+    return(src - osrc - 1); /* count does not include NUL */
+}
+
+/*
+ * Appends src to string dst of size dsize (unlike strncat, dsize is the
+ * full size of dst, not space left).  At most dsize-1 characters
+ * will be copied.  Always NUL terminates (unless dsize <= strlen(dst)).
+ * Returns strlen(src) + MIN(dsize, strlen(initial dst)).
+ * If retval >= dsize, truncation occurred.
+ */
+size_t
+redis_strlcat(char *dst, const char *src, size_t dsize)
+{
+    const char *odst = dst;
+    const char *osrc = src;
+    size_t n = dsize;
+    size_t dlen;
+
+    /* Find the end of dst and adjust bytes left but don't go past end. */
+    while (n-- != 0 && *dst != '\0')
+        dst++;
+    dlen = dst - odst;
+    n = dsize - dlen;
+
+    if (n-- == 0)
+        return(dlen + strlen(src));
+    while (*src != '\0') {
+        if (n != 0) {
+            *dst++ = *src;
+            n--;
+        }
+        src++;
+    }
+    *dst = '\0';
+
+    return(dlen + (src - osrc));    /* count does not include NUL */
+}
+
+
+
+
+