diff options
| author | Alain Knaff <alain@knaff.lu> | 2008-11-10 17:08:08 -0800 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2009-01-05 11:53:07 -0500 |
| commit | 5b6f1eb97d462a45be3b30759758b5fdbb562c8c (patch) | |
| tree | e8f664c34dde71b95955f57caad3093581be87ef | |
| parent | 7d3b56ba37a95f1f370f50258ed3954c304c524b (diff) | |
vfs: lseek(fd, 0, SEEK_CUR) race condition
This patch fixes a race condition in lseek. While it is expected that
unpredictable behaviour may result while repositioning the offset of a
file descriptor concurrently with reading/writing to the same file
descriptor, this should not happen when merely *reading* the file
descriptor's offset.
Unfortunately, the only portable way in Unix to read a file
descriptor's offset is lseek(fd, 0, SEEK_CUR); however executing this
concurrently with read/write may mess up the position.
[with fixes from akpm]
Signed-off-by: Alain Knaff <alain@knaff.lu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| -rw-r--r-- | fs/read_write.c | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/fs/read_write.c b/fs/read_write.c index 969a6d9c020..5cc6924eb15 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -50,6 +50,14 @@ generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin) offset += inode->i_size; break; case SEEK_CUR: + /* + * Here we special-case the lseek(fd, 0, SEEK_CUR) + * position-querying operation. Avoid rewriting the "same" + * f_pos value back to the file because a concurrent read(), + * write() or lseek() might have altered it + */ + if (offset == 0) + return file->f_pos; offset += file->f_pos; break; } @@ -105,6 +113,10 @@ loff_t default_llseek(struct file *file, loff_t offset, int origin) offset += i_size_read(file->f_path.dentry->d_inode); break; case SEEK_CUR: + if (offset == 0) { + retval = file->f_pos; + goto out; + } offset += file->f_pos; } retval = -EINVAL; @@ -115,6 +127,7 @@ loff_t default_llseek(struct file *file, loff_t offset, int origin) } retval = offset; } +out: unlock_kernel(); return retval; } |