lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [day] [month] [year] [list]
Date:   Fri, 20 Nov 2020 17:14:29 -0600
From:   "Eric W. Biederman" <>
        Linus Torvalds <>,
        Alexander Viro <>,
        Christian Brauner <>,
        Oleg Nesterov <>,
        Cyrill Gorcunov <>,
        Jann Horn <>, Kees Cook <>,
        Daniel P . Berrangé <>,
        Jeff Layton <>,
        Miklos Szeredi <>,
        Matthew Wilcox <>,
        "J. Bruce Fields" <>,
        Trond Myklebust <>,
        Chris Wright <>,
        Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Martin KaFai Lau <>,
        Song Liu <>, Yonghong Song <>,
        Andrii Nakryiko <>,
        John Fastabend <>,
        KP Singh <>,
        "Eric W. Biederman" <>
Subject: [PATCH v2 12/24] proc/fd: In tid_fd_mode use task_lookup_fd_rcu

When discussing[1] exec and posix file locks it was realized that none
of the callers of get_files_struct fundamentally needed to call
get_files_struct, and that by switching them to helper functions
instead it will both simplify their code and remove unnecessary
increments of files_struct.count.  Those unnecessary increments can
result in exec unnecessarily unsharing files_struct which breaking
posix locks, and it can result in fget_light having to fallback to
fget reducing system performance.

Instead of manually coding finding the files struct for a task and
then calling files_lookup_fd_rcu, use the helper task_lookup_fd_rcu
that combines those to steps.   Making the code simpler and removing
the need to get a reference on a files_struct.

Suggested-by: Oleg Nesterov <>
Acked-by: Christian Brauner <>
Signed-off-by: "Eric W. Biederman" <>
 fs/proc/fd.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 3dec44d7c5c5..c1a984f3c4df 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -83,18 +83,13 @@ static const struct file_operations proc_fdinfo_file_operations = {
 static bool tid_fd_mode(struct task_struct *task, unsigned fd, fmode_t *mode)
-	struct files_struct *files = get_files_struct(task);
 	struct file *file;
-	if (!files)
-		return false;
-	file = files_lookup_fd_rcu(files, fd);
+	file = task_lookup_fd_rcu(task, fd);
 	if (file)
 		*mode = file->f_mode;
-	put_files_struct(files);
 	return !!file;

Powered by blists - more mailing lists