linux-kernel - [PATCH] /proc/self/maps doesn't display the real file offset

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Date:	Wed, 13 Aug 2008 19:56:12 +0200
From:	cboulte@...il.com
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org
Subject: [PATCH] /proc/self/maps doesn't display the real file offset

2.6.26 kernel on i386 platform.

http://bugzilla.kernel.org/show_bug.cgi?id=11318

In function show_map (file: fs/proc/task_mmu.c), if vma->vm_pgoff >
2^20 than (vma->vm_pgoff << PAGE_SIZE) is greater than 2^32 (with
PAGE_SIZE equal to 4096 (i.e. 2^12). The next seq_printf use an
unsigned long for the conversion of (vma->vm_pgoff << PAGE_SIZE), as a
result the offset value displayed in /proc/self/maps is truncated if
the page offset is greater than 2^20.

A test that show this issue:

#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

#define PAGE_SIZE (getpagesize())

#if __i386__
#   define U64_STR "%llx"
#elif __x86_64
#   define U64_STR "%lx"
#else
#   error "Architecture Unsupported"
#endif

int main(int argc, char *argv[])
{
	int fd;
	char *addr;
	off64_t offset = 0x10000000;
	char *filename = "/dev/zero";

	fd = open(filename, O_RDONLY);
	if (fd < 0) {
		perror("open");
		return 1;
	}

	offset *= 0x10;
	printf("offset = " U64_STR "\n", offset);

	addr = (char*)mmap64(NULL, PAGE_SIZE, PROT_READ, MAP_PRIVATE, fd,
			     offset);
	if ((void*)addr == MAP_FAILED) {
		perror("mmap64");
		return 1;
	}

	{
		FILE *fmaps;
		char *line = NULL;
		size_t len = 0;
		ssize_t read;
		size_t filename_len = strlen(filename);

		fmaps = fopen("/proc/self/maps", "r");
		if (!fmaps) {
			perror("fopen");
			return 1;
		}
		while ((read = getline(&line, &len, fmaps)) != -1) {
			if ((read > filename_len + 1)
			    && (strncmp(&line[read - filename_len - 1], filename,
filename_len) == 0))
				printf("%s", line);
		}

		if (line)
			free(line);

		fclose(fmaps);
	}

	close(fd);
	return 0;
}

Signed-off-by: Clement Calmels <cboulte@...il.com>
---
 fs/proc/nommu.c    |    4 ++--
 fs/proc/task_mmu.c |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6.26/fs/proc/task_mmu.c
===================================================================
--- linux-2.6.26.orig/fs/proc/task_mmu.c
+++ linux-2.6.26/fs/proc/task_mmu.c
@@ -219,14 +219,14 @@ static int show_map(struct seq_file *m,
 		ino = inode->i_ino;
 	}

-	seq_printf(m, "%08lx-%08lx %c%c%c%c %08lx %02x:%02x %lu %n",
+	seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
 			vma->vm_start,
 			vma->vm_end,
 			flags & VM_READ ? 'r' : '-',
 			flags & VM_WRITE ? 'w' : '-',
 			flags & VM_EXEC ? 'x' : '-',
 			flags & VM_MAYSHARE ? 's' : 'p',
-			vma->vm_pgoff << PAGE_SHIFT,
+		        ((loff_t) vma->vm_pgoff) << PAGE_SHIFT,
 			MAJOR(dev), MINOR(dev), ino, &len);

 	/*
Index: linux-2.6.26/fs/proc/nommu.c
===================================================================
--- linux-2.6.26.orig/fs/proc/nommu.c
+++ linux-2.6.26/fs/proc/nommu.c
@@ -52,14 +52,14 @@ int nommu_vma_show(struct seq_file *m, s
 	}

 	seq_printf(m,
-		   "%08lx-%08lx %c%c%c%c %08lx %02x:%02x %lu %n",
+		   "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
 		   vma->vm_start,
 		   vma->vm_end,
 		   flags & VM_READ ? 'r' : '-',
 		   flags & VM_WRITE ? 'w' : '-',
 		   flags & VM_EXEC ? 'x' : '-',
 		   flags & VM_MAYSHARE ? flags & VM_SHARED ? 'S' : 's' : 'p',
-		   vma->vm_pgoff << PAGE_SHIFT,
+		   ((loff_t)vma->vm_pgoff) << PAGE_SHIFT,
 		   MAJOR(dev), MINOR(dev), ino, &len);

 	if (file) {
--
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