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authorKirill Smelkov <kirr@nexedi.com>2019-04-12 12:31:57 +0300
committerKirill Smelkov <kirr@nexedi.com>2019-05-06 17:46:52 +0300
commit438ab720c675a16d53bb18f76a94d25bbe420c45 (patch)
treef84b1009eb6918a07252b22089dde736cf2ff6d3 /fs/open.c
parentc5bf68fe0c86a5835bd2e6aead1c49976360753f (diff)
vfs: pass ppos=NULL to .read()/.write() of FMODE_STREAM files
This amends commit 10dce8af3422 ("fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock") in how position is passed into .read()/.write() handler for stream-like files: Rasmus noticed that we currently pass 0 as position and ignore any position change if that is done by a file implementation. This papers over bugs if ppos is used in files that declare themselves as being stream-like as such bugs will go unnoticed. Even if a file implementation is correctly converted into using stream_open, its read/write later could be changed to use ppos and even though that won't be working correctly, that bug might go unnoticed without someone doing wrong behaviour analysis. It is thus better to pass ppos=NULL into read/write for stream-like files as that don't give any chance for ppos usage bugs because it will oops if ppos is ever used inside .read() or .write(). Note 1: rw_verify_area, new_sync_{read,write} needs to be updated because they are called by vfs_read/vfs_write & friends before file_operations .read/.write . Note 2: if file backend uses new-style .read_iter/.write_iter, position is still passed into there as non-pointer kiocb.ki_pos . Currently stream_open.cocci (semantic patch added by 10dce8af3422) ignores files whose file_operations has *_iter methods. Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
Diffstat (limited to 'fs/open.c')
-rw-r--r--fs/open.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/fs/open.c b/fs/open.c
index a00350018a47..9c7d724a6f67 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1219,8 +1219,9 @@ EXPORT_SYMBOL(nonseekable_open);
/*
* stream_open is used by subsystems that want stream-like file descriptors.
* Such file descriptors are not seekable and don't have notion of position
- * (file.f_pos is always 0). Contrary to file descriptors of other regular
- * files, .read() and .write() can run simultaneously.
+ * (file.f_pos is always 0 and ppos passed to .read()/.write() is always NULL).
+ * Contrary to file descriptors of other regular files, .read() and .write()
+ * can run simultaneously.
*
* stream_open never fails and is marked to return int so that it could be
* directly used as file_operations.open .