Avoid SIGBUS on mmap failure

mmap will fail with SIGBUS if trying to map a non-existent portion of
a file. While this should never happen with /dev/mem, it can happen if
passing a regular file with option -d. While people should no longer
do that, failure gracefully seems better than crashing. So check for
the file size before calling mmap.

This closes bug #46066:
http://savannah.nongnu.org/bugs/?46066

1 files changed, 21 insertions, 0 deletions

diff --git a/util.c b/util.c
index 8cafe5c..5795d02 100644
--- a/util.c
+++ b/util.c
@@ -152,6 +152,7 @@ void *mem_chunk(off_t base, size_t len, const char *devmem)
 	void *p;
 	int fd;
 #ifdef USE_MMAP
+	struct stat statbuf;
 	off_t mmoffset;
 	void *mmp;
 #endif
@@ -169,6 +170,26 @@ void *mem_chunk(off_t base, size_t len, const char *devmem)
 	}
 
 #ifdef USE_MMAP
+	if (fstat(fd, &statbuf) == -1)
+	{
+		fprintf(stderr, "%s: ", devmem);
+		perror("stat");
+		free(p);
+		return NULL;
+	}
+
+	/*
+	 * mmap() will fail with SIGBUS if trying to map beyond the end of
+	 * the file.
+	 */
+	if (S_ISREG(statbuf.st_mode) && base + (off_t)len > statbuf.st_size)
+	{
+		fprintf(stderr, "mmap: Can't map beyond end of file %s\n",
+			devmem);
+		free(p);
+		return NULL;
+	}
+
 #ifdef _SC_PAGESIZE
 	mmoffset = base % sysconf(_SC_PAGESIZE);
 #else