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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: Tejun Heo <tj@kernel.org>
Acked-by: Hugh Dickins <hugh@veritas.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tejun Heo 2008-09-03 16:09:47 +02:00 committed by Linus Torvalds
parent d210baf53b
commit ce36394269
1 changed files with 4 additions and 0 deletions
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4
mm/mmap.c
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@ -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: