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Subject[PATCH #2.6.27-rc5] 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>
---
mm/mmap.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 339cf5c..e7a5a68 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -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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