On Wed, Aug 28, 2024 at 12:15:40PM GMT, Alejandro Colomar wrote: > Hi Yafang, > > On Wed, Aug 28, 2024 at 11:03:14AM GMT, Yafang Shao wrote: > > We want to eliminate the use of __get_task_comm() for the following > > reasons: > > > > - The task_lock() is unnecessary > > Quoted from Linus [0]: > > : Since user space can randomly change their names anyway, using locking > > : was always wrong for readers (for writers it probably does make sense > > : to have some lock - although practically speaking nobody cares there > > : either, but at least for a writer some kind of race could have > > : long-term mixed results > > > > - The BUILD_BUG_ON() doesn't add any value > > The only requirement is to ensure that the destination buffer is a valid > > array. > > > > - Zeroing is not necessary in current use cases > > To avoid confusion, we should remove it. Moreover, not zeroing could > > potentially make it easier to uncover bugs. If the caller needs a > > zero-padded task name, it should be explicitly handled at the call site. > > > > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Link: https://lore.kernel.org/all/CAHk-=wivfrF0_zvf+oj6==Sh=-npJooP8chLPEfaFV0oNYTTBA@xxxxxxxxxxxxxx [0] > > Link: https://lore.kernel.org/all/CAHk-=whWtUC-AjmGJveAETKOMeMFSTwKwu99v7+b6AyHMmaDFA@xxxxxxxxxxxxxx/ > > Suggested-by: Alejandro Colomar <alx@xxxxxxxxxx> > > Link: https://lore.kernel.org/all/2jxak5v6dfxlpbxhpm3ey7oup4g2lnr3ueurfbosf5wdo65dk4@srb3hsk72zwq > > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> > > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> > > Cc: Christian Brauner <brauner@xxxxxxxxxx> > > Cc: Jan Kara <jack@xxxxxxx> > > Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx> > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > Cc: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> > > Cc: Matus Jokay <matus.jokay@xxxxxxxx> > > Cc: Alejandro Colomar <alx@xxxxxxxxxx> > > Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx> > > --- > > fs/exec.c | 10 ---------- > > fs/proc/array.c | 2 +- > > include/linux/sched.h | 32 ++++++++++++++++++++++++++------ > > kernel/kthread.c | 2 +- > > 4 files changed, 28 insertions(+), 18 deletions(-) > > > > [...] > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index f8d150343d42..c40b95a79d80 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > [...] > > > @@ -1914,10 +1917,27 @@ static inline void set_task_comm(struct task_struct *tsk, const char *from) > > __set_task_comm(tsk, from, false); > > } > > > > -extern char *__get_task_comm(char *to, size_t len, struct task_struct *tsk); > > +/* > > [...] > > > + * - ARRAY_SIZE() can help ensure that @buf is indeed an array. > > + */ > > #define get_task_comm(buf, tsk) ({ \ > > - BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \ > > - __get_task_comm(buf, sizeof(buf), tsk); \ > > + strscpy(buf, (tsk)->comm, ARRAY_SIZE(buf)); \ > > I see that there's a two-argument macro > > #define strscpy(dst, src) sized_strscpy(dst, src, sizeof(dst)) > > which is used in patch 2/8 > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > index 6f0d6fb6523f..e4ef5e57dde9 100644 > --- a/kernel/auditsc.c > +++ b/kernel/auditsc.c > @@ -2730,7 +2730,7 @@ void __audit_ptrace(struct task_struct *t) > context->target_uid = task_uid(t); > context->target_sessionid = audit_get_sessionid(t); > security_task_getsecid_obj(t, &context->target_sid); > - memcpy(context->target_comm, t->comm, TASK_COMM_LEN); > + strscpy(context->target_comm, t->comm); > } > > /** Ahh, the actual generic definition is in <include/linux/string.h>. You could do diff --git i/include/linux/string.h w/include/linux/string.h index 9edace076ddb..060504719904 100644 --- i/include/linux/string.h +++ w/include/linux/string.h @@ -76,11 +76,11 @@ ssize_t sized_strscpy(char *, const char *, size_t); * known size. */ #define __strscpy0(dst, src, ...) \ - sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst)) + sized_strscpy(dst, src, ARRAY_SIZE(dst)) #define __strscpy1(dst, src, size) sized_strscpy(dst, src, size) #define __strscpy_pad0(dst, src, ...) \ - sized_strscpy_pad(dst, src, sizeof(dst) + __must_be_array(dst)) + sized_strscpy_pad(dst, src, ARRAY_SIZE(dst)) #define __strscpy_pad1(dst, src, size) sized_strscpy_pad(dst, src, size) /** > > I propose modifying that macro to use ARRAY_SIZE() instead of sizeof(), > and then calling that macro here too. That would not only make sure > that this is an array, but make sure that every call to that macro is an > array. An if there are macros for similar string functions that reduce > the argument with a usual sizeof(), the same thing could be done to > those too. > > Have a lovley day! > Alex > > > + buf; \ > > }) > > > > #ifdef CONFIG_SMP > > diff --git a/kernel/kthread.c b/kernel/kthread.c > > index f7be976ff88a..7d001d033cf9 100644 > > --- a/kernel/kthread.c > > +++ b/kernel/kthread.c > > @@ -101,7 +101,7 @@ void get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk) > > struct kthread *kthread = to_kthread(tsk); > > > > if (!kthread || !kthread->full_name) { > > - __get_task_comm(buf, buf_size, tsk); > > + strscpy(buf, tsk->comm, buf_size); > > return; > > } > > > > -- > > 2.43.5 > > > > -- > <https://www.alejandro-colomar.es/> -- <https://www.alejandro-colomar.es/>
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