sk_fgetsize to not use ftell.

The previous version of sk_fgetsize used ftell and fseek to compute
the size of a file. There are so many issues with this that it is called
out by securecoding.cert.org as FIO19-C as a thing not to do. We already
have correct code for computing the size of a file in the mmap code, so
use that instead.

Change-Id: I1d771124989d0ec1523f6d858814ee563263213a
Reviewed-on: https://skia-review.googlesource.com/9860
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/src/ports/SkOSFile_posix.cpp b/src/ports/SkOSFile_posix.cpp
index 48b5b95ad3..40028246ff 100644
--- a/src/ports/SkOSFile_posix.cpp
+++ b/src/ports/SkOSFile_posix.cpp
@@ -19,6 +19,25 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+size_t sk_fgetsize(FILE* f) {
+    int fd = fileno(f);
+    if (fd < 0) {
+        return 0;
+    }
+
+    struct stat status;
+    if (0 != fstat(fd, &status)) {
+        return 0;
+    }
+    if (!S_ISREG(status.st_mode)) {
+        return 0;
+    }
+    if (!SkTFitsIn<size_t>(status.st_size)) {
+        return 0;
+    }
+    return static_cast<size_t>(status.st_size);
+}
+
 bool sk_exists(const char *path, SkFILE_Flags flags) {
     int mode = F_OK;
     if (flags & kRead_SkFILE_Flag) {