Replace mmap with xmmap, better handling MAP_FAILED.

In some cases we did not even bother to check the return value of
mmap() and just assume it worked.  This is bad, because if we are
out of virtual address space the kernel returned MAP_FAILED and we
would attempt to dereference that address, segfaulting without any
real error output to the user.

We are replacing all calls to mmap() with xmmap() and moving all
MAP_FAILED checking into that single location.  If a mmap call
fails we try to release enough least-recently-used pack windows
to possibly succeed, then retry the mmap() attempt.  If we cannot
mmap even after releasing pack memory then we die() as none of our
callers have any reasonable recovery strategy for a failed mmap.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 5 insertions, 13 deletions

diff --git a/sha1_file.c b/sha1_file.c
index fb1032b0f..84037fe98 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -355,10 +355,8 @@ static void read_info_alternates(const char * relative_base, int depth)
 		close(fd);
 		return;
 	}
-	map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	map = xmmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	close(fd);
-	if (map == MAP_FAILED)
-		return;
 
 	link_alt_odb_entries(map, map + st.st_size, '\n', relative_base, depth);
 
@@ -442,10 +440,8 @@ static int check_packed_git_idx(const char *path, unsigned long *idx_size_,
 		return -1;
 	}
 	idx_size = st.st_size;
-	idx_map = mmap(NULL, idx_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	idx_map = xmmap(NULL, idx_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	close(fd);
-	if (idx_map == MAP_FAILED)
-		return -1;
 
 	index = idx_map;
 	*idx_map_ = idx_map;
@@ -630,7 +626,7 @@ unsigned char* use_pack(struct packed_git *p,
 			while (packed_git_limit < pack_mapped
 				&& unuse_one_window(p))
 				; /* nothing */
-			win->base = mmap(NULL, win->len,
+			win->base = xmmap(NULL, win->len,
 				PROT_READ, MAP_PRIVATE,
 				p->pack_fd, win->offset);
 			if (win->base == MAP_FAILED)
@@ -828,10 +824,8 @@ void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 		 */
 		sha1_file_open_flag = 0;
 	}
-	map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	map = xmmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	close(fd);
-	if (map == MAP_FAILED)
-		return NULL;
 	*size = st.st_size;
 	return map;
 }
@@ -1987,10 +1981,8 @@ int index_fd(unsigned char *sha1, int fd, struct stat *st, int write_object, con
 
 	buf = "";
 	if (size)
-		buf = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+		buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
 	close(fd);
-	if (buf == MAP_FAILED)
-		return -1;
 
 	if (!type)
 		type = blob_type;