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Howlett" , Suren Baghdasaryan , Vlastimil Babka , pedro.falcato@gmail.com, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/3] pidfd: extend pidfd_get_pid() and de-duplicate pid lookup Date: Thu, 10 Oct 2024 19:15:43 +0100 Message-ID: <8e7edaf2f648fb01a71def749f17f76c0502dee1.1728578231.git.lorenzo.stoakes@oracle.com> X-Mailer: git-send-email 2.46.2 In-Reply-To: References: X-ClientProxiedBy: LO4P123CA0595.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:295::12) To SJ0PR10MB5613.namprd10.prod.outlook.com (2603:10b6:a03:3d0::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ0PR10MB5613:EE_|SJ2PR10MB7826:EE_ X-MS-Office365-Filtering-Correlation-Id: 4b3ad6ea-a3d5-41eb-b55b-08dce95792d7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|366016; X-Microsoft-Antispam-Message-Info: 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 O9BQS9ZR F+jsPEdFmlJ5pzgvTbHsZ8zdPpfyC5f9HYsUn6nyN+czjZZCOa9HKenaIsWs2uW6hNomjDrMPsZDyRLxwQnMzLw6QRCC4th/w5M41aghQS2GXzHRblCv2i00Ps8c2ACp6yePqSUdM8xwbzKM/U1f//KkBHvNwNVAkKEf5U+s6wYZQO0KrzZL2p/7EkLgKdp66VXOBrn0XqbzSWkDugOycbY3rC6w1lvvMSmaxk/BELz9BO+REEAWjBVcNIi/9uW1DQ6qtSHP44CsbUyBQredM9ohkaVc5VVWy6QFbd6M2zjzAlXevTFRSbVAcl3sdXdxOH5sTbEXh0aKUieXYs9NQqmqvfVx2hDD/7hX13f1xLCIf6T/M+FNXmEKBL9vuf41kKQh+gstL1GvmUAAbXu3mThE1Oc9E/hqb6+XpqAw4M2PtCrNNVuIMGR1rRFixhmeHzRZtEcH0cGbNDvXTCvgpCZRznYr4pJBn1Var75Tjl+qXmvvzxrqYzPL4QERHC/3oUTzBv/DTMFpfq34suIytdooHD+D2z+vwJSiG4vopMYgxcgw9MdVgzgBJORGH4srzsNhWDHoGl9m4RuY00g1nR5pDqqF5E/oaMuNbEIbEmZgqYpV+bZkCPnaG7Arj1MeV/i3ffYHGGTlJtQM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The means by which a pid is determined from a pidfd is duplicated, with some callers holding a reference to the (pid)fd, and others explicitly pinning the pid. Introduce __pidfd_get_pid() which abstracts both approaches and provide optional output parameters for file->f_flags and the fd (the latter of which, if provided, prevents the function from decrementing the fd's refernce count). Additionally, allow the ability to open a pidfd by opening a /proc/ directory, utilised by the pidfd_send_signal() system call, providing a pidfd_get_pid_proc() helper function to do so. Doing this allows us to eliminate open-coded pidfd pid lookup and to consistently handle this in one place. This lays the groundwork for a subsequent patch which adds a new sentinel pidfd to explicitly reference the current process (i.e. thread group leader) without the need for a pidfd. Signed-off-by: Lorenzo Stoakes --- include/linux/pid.h | 42 +++++++++++++++++++++++++++++++- kernel/pid.c | 58 ++++++++++++++++++++++++++++++--------------- kernel/signal.c | 22 ++++------------- 3 files changed, 84 insertions(+), 38 deletions(-) diff --git a/include/linux/pid.h b/include/linux/pid.h index a3aad9b4074c..68b02eab7509 100644 --- a/include/linux/pid.h +++ b/include/linux/pid.h @@ -2,6 +2,7 @@ #ifndef _LINUX_PID_H #define _LINUX_PID_H +#include #include #include #include @@ -72,8 +73,47 @@ extern struct pid init_struct_pid; struct file; + +/** + * __pidfd_get_pid() - Retrieve a pid associated with the specified pidfd. + * + * @pidfd: The pidfd whose pid we want, or the fd of a /proc/ file if + * @alloc_proc is also set. + * @pin_pid: If set, then the reference counter of the returned pid is + * incremented. If not set, then @fd should be provided to pin the + * pidfd. + * @allow_proc: If set, then an fd of a /proc/ file can be passed instead + * of a pidfd, and this will be used to determine the pid. + * @flags: Output variable, if non-NULL, then the file->f_flags of the + * pidfd will be set here. + * @fd: Output variable, if non-NULL, then the pidfd reference will + * remain elevated and the caller will need to decrement it + * themselves. + * + * Returns: If successful, the pid associated with the pidfd, otherwise an + * error. + */ +struct pid *__pidfd_get_pid(unsigned int pidfd, bool pin_pid, + bool allow_proc, unsigned int *flags, + struct fd *fd); + +static inline struct pid *pidfd_get_pid(unsigned int pidfd, unsigned int *flags) +{ + return __pidfd_get_pid(pidfd, /* pin_pid = */ true, + /* allow_proc = */ false, + flags, /* fd = */ NULL); +} + +static inline struct pid *pidfd_to_pid_proc(unsigned int pidfd, + unsigned int *flags, + struct fd *fd) +{ + return __pidfd_get_pid(pidfd, /* pin_pid = */ false, + /* allow_proc = */ true, + flags, fd); +} + struct pid *pidfd_pid(const struct file *file); -struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags); struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags); int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret); void do_notify_pidfd(struct task_struct *task); diff --git a/kernel/pid.c b/kernel/pid.c index 2715afb77eab..25cc1c36a1b1 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include #include @@ -534,22 +535,46 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns) } EXPORT_SYMBOL_GPL(find_ge_pid); -struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags) +struct pid *__pidfd_get_pid(unsigned int pidfd, bool pin_pid, + bool allow_proc, unsigned int *flags, + struct fd *fd) { - struct fd f; + struct file *file; struct pid *pid; + struct fd f = fdget(pidfd); - f = fdget(fd); - if (!fd_file(f)) + file = fd_file(f); + if (!file) return ERR_PTR(-EBADF); - pid = pidfd_pid(fd_file(f)); - if (!IS_ERR(pid)) { - get_pid(pid); - *flags = fd_file(f)->f_flags; + pid = pidfd_pid(file); + /* If we allow opening a pidfd via /proc/, do so. */ + if (IS_ERR(pid) && allow_proc) + pid = tgid_pidfd_to_pid(file); + + if (IS_ERR(pid)) { + fdput(f); + return pid; } - fdput(f); + if (pin_pid) + get_pid(pid); + else + WARN_ON_ONCE(!fd); /* Nothing to keep pid/pidfd around? */ + + if (flags) + *flags = file->f_flags; + + /* + * If the user provides an fd output then it will handle decrementing + * its reference counter. + */ + if (fd) + *fd = f; + else + /* Otherwise we release it. */ + fdput(f); + return pid; } @@ -747,23 +772,18 @@ SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd, unsigned int, flags) { struct pid *pid; - struct fd f; int ret; /* flags is currently unused - make sure it's unset */ if (flags) return -EINVAL; - f = fdget(pidfd); - if (!fd_file(f)) - return -EBADF; - - pid = pidfd_pid(fd_file(f)); + pid = pidfd_get_pid(pidfd, NULL); if (IS_ERR(pid)) - ret = PTR_ERR(pid); - else - ret = pidfd_getfd(pid, fd); + return PTR_ERR(pid); - fdput(f); + ret = pidfd_getfd(pid, fd); + + put_pid(pid); return ret; } diff --git a/kernel/signal.c b/kernel/signal.c index 4344860ffcac..868bfa674c62 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3875,17 +3875,6 @@ static int copy_siginfo_from_user_any(kernel_siginfo_t *kinfo, return copy_siginfo_from_user(kinfo, info); } -static struct pid *pidfd_to_pid(const struct file *file) -{ - struct pid *pid; - - pid = pidfd_pid(file); - if (!IS_ERR(pid)) - return pid; - - return tgid_pidfd_to_pid(file); -} - #define PIDFD_SEND_SIGNAL_FLAGS \ (PIDFD_SIGNAL_THREAD | PIDFD_SIGNAL_THREAD_GROUP | \ PIDFD_SIGNAL_PROCESS_GROUP) @@ -3908,10 +3897,11 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, siginfo_t __user *, info, unsigned int, flags) { int ret; - struct fd f; struct pid *pid; kernel_siginfo_t kinfo; enum pid_type type; + unsigned int f_flags; + struct fd f; /* Enforce flags be set to 0 until we add an extension. */ if (flags & ~PIDFD_SEND_SIGNAL_FLAGS) @@ -3921,12 +3911,8 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, if (hweight32(flags & PIDFD_SEND_SIGNAL_FLAGS) > 1) return -EINVAL; - f = fdget(pidfd); - if (!fd_file(f)) - return -EBADF; - /* Is this a pidfd? */ - pid = pidfd_to_pid(fd_file(f)); + pid = pidfd_to_pid_proc(pidfd, &f_flags, &f); if (IS_ERR(pid)) { ret = PTR_ERR(pid); goto err; @@ -3939,7 +3925,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, switch (flags) { case 0: /* Infer scope from the type of pidfd. */ - if (fd_file(f)->f_flags & PIDFD_THREAD) + if (f_flags & PIDFD_THREAD) type = PIDTYPE_PID; else type = PIDTYPE_TGID;