Commit ce363942 authored by Tejun Heo's avatar Tejun Heo Committed by Linus Torvalds

mmap: fix petty bug in anonymous shared mmap offset handling

Anonymous mappings should ignore offset but shared anonymous mapping
forgot to clear it and makes the following legit test program trigger
SIGBUS.

 #include <sys/mman.h>
 #include <stdio.h>
 #include <errno.h>

 #define PAGE_SIZE	4096

 int main(void)
 {
	 char *p;
	 int i;

	 p = mmap(NULL, 2 * PAGE_SIZE, PROT_READ|PROT_WRITE,
		  MAP_SHARED|MAP_ANONYMOUS, -1, PAGE_SIZE);
	 if (p == MAP_FAILED) {
		 perror("mmap");
		 return 1;
	 }

	 for (i = 0; i < 2; i++) {
		 printf("page %d\n", i);
		 p[i * 4096] = i;
	 }
	 return 0;
 }

Fix it.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarHugh Dickins <hugh@veritas.com>
Acked-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d210baf5
......@@ -1030,6 +1030,10 @@ unsigned long do_mmap_pgoff(struct file * file, unsigned long addr,
} else {
switch (flags & MAP_TYPE) {
case MAP_SHARED:
/*
* Ignore pgoff.
*/
pgoff = 0;
vm_flags |= VM_SHARED | VM_MAYSHARE;
break;
case MAP_PRIVATE:
......
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