vfs: introduce FMODE_UNSIGNED_OFFSET for allowing negative f_pos

Now, rw_verify_area() checsk f_pos is negative or not.  And if negative,
returns -EINVAL.

But, some special files as /dev/(k)mem and /proc/<pid>/mem etc..  has
negative offsets.  And we can't do any access via read/write to the
file(device).

So introduce FMODE_UNSIGNED_OFFSET to allow negative file offsets.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index e985b1c2730e800db599ad445371a8b100eee506..1256454b2d4364f7fa6ad95b661d30ad62b673b4 100644 (file)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -876,6 +876,10 @@ static int memory_open(struct inode *inode, struct file *filp)
        if (dev->dev_info)
                filp->f_mapping->backing_dev_info = dev->dev_info;
 
+       /* Is /dev/mem or /dev/kmem ? */
+       if (dev->dev_info == &directly_mappable_cdev_bdi)
+               filp->f_mode |= FMODE_UNSIGNED_OFFSET;
+
        if (dev->fops->open)
                return dev->fops->open(inode, filp);
 

diff --git a/fs/proc/base.c b/fs/proc/base.c
index dc5d5f51f3fe4dc564a19e06cb330d09abc9b6a4..fb2a5abd4e4facfb83cd9ec0831f6ca11cace34c 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -771,6 +771,8 @@ static const struct file_operations proc_single_file_operations = {
 static int mem_open(struct inode* inode, struct file* file)
 {
        file->private_data = (void*)((long)current->self_exec_id);
+       /* OK to pass negative loff_t, we can catch out-of-range */
+       file->f_mode |= FMODE_UNSIGNED_OFFSET;
        return 0;
 }
 

diff --git a/fs/read_write.c b/fs/read_write.c
index e757ef26e4cecb6d47fd628b32f204e90c4b8497..9cd9d148105d287b55c9f60af4034f300cc6d1af 100644 (file)
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -31,6 +31,20 @@ const struct file_operations generic_ro_fops = {
 
 EXPORT_SYMBOL(generic_ro_fops);
 
+static int
+__negative_fpos_check(struct file *file, loff_t pos, size_t count)
+{
+       /*
+        * pos or pos+count is negative here, check overflow.
+        * too big "count" will be caught in rw_verify_area().
+        */
+       if ((pos < 0) && (pos + count < pos))
+               return -EOVERFLOW;
+       if (file->f_mode & FMODE_UNSIGNED_OFFSET)
+               return 0;
+       return -EINVAL;
+}
+
 /**
  * generic_file_llseek_unlocked - lockless generic llseek implementation
  * @file:      file structure to seek on
@@ -62,7 +76,9 @@ generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin)
                break;
        }
 
-       if (offset < 0 || offset > inode->i_sb->s_maxbytes)
+       if (offset < 0 && __negative_fpos_check(file, offset, 0))
+               return -EINVAL;
+       if (offset > inode->i_sb->s_maxbytes)
                return -EINVAL;
 
        /* Special lock needed here? */
@@ -137,7 +153,7 @@ loff_t default_llseek(struct file *file, loff_t offset, int origin)
                        offset += file->f_pos;
        }
        retval = -EINVAL;
-       if (offset >= 0) {
+       if (offset >= 0 || !__negative_fpos_check(file, offset, 0)) {
                if (offset != file->f_pos) {
                        file->f_pos = offset;
                        file->f_version = 0;
@@ -221,6 +237,7 @@ bad:
 }
 #endif
 
+
 /*
  * rw_verify_area doesn't like huge counts. We limit
  * them to something that fits in "int" so that others
@@ -238,8 +255,11 @@ int rw_verify_area(int read_write, struct file *file, loff_t *ppos, size_t count
        if (unlikely((ssize_t) count < 0))
                return retval;
        pos = *ppos;
-       if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
-               return retval;
+       if (unlikely((pos < 0) || (loff_t) (pos + count) < 0)) {
+               retval = __negative_fpos_check(file, pos, count);
+               if (retval)
+                       return retval;
+       }
 
        if (unlikely(inode->i_flock && mandatory_lock(inode))) {
                retval = locks_mandatory_area(

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0cd6821013a05849bca9fdff5e5f6ab11885aec9..7fc126df1c42c0c029095f3262acdde358e95436 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -92,6 +92,9 @@ struct inodes_stat_t {
 /* Expect random access pattern */
 #define FMODE_RANDOM           ((__force fmode_t)0x1000)
 
+/* File is huge (eg. /dev/kmem): treat loff_t as unsigned */
+#define FMODE_UNSIGNED_OFFSET  ((__force fmode_t)0x2000)
+
 /* File was opened by fanotify and shouldn't generate fanotify events */
 #define FMODE_NONOTIFY         ((__force fmode_t)0x1000000)