Commit 9d65cb4a authored by Alexey Dobriyan's avatar Alexey Dobriyan Committed by Linus Torvalds
Browse files

Fix race between cat /proc/*/wchan and rmmod et al 



kallsyms_lookup() can go iterating over modules list unprotected which is OK
for emergency situations (oops), but not OK for regular stuff like
/proc/*/wchan.

Introduce lookup_symbol_name()/lookup_module_symbol_name() which copy symbol
name into caller-supplied buffer or return -ERANGE.  All copying is done with
module_mutex held, so...

Signed-off-by: default avatarAlexey Dobriyan <adobriyan@sw.ru>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ffb45122

fs/proc/base.c

+5 −6
Original line number Diff line number Diff line
@@ -278,16 +278,15 @@ static int proc_pid_auxv(struct task_struct *task, char *buffer) 
 */

static int proc_pid_wchan(struct task_struct *task, char *buffer)

{

	const char *sym_name;

	unsigned long wchan;

	char namebuf[KSYM_NAME_LEN+1];

	char symname[KSYM_NAME_LEN+1];



	wchan = get_wchan(task);



	sym_name = kallsyms_lookup(wchan, NULL, NULL, NULL, namebuf);

	if (sym_name)

		return sprintf(buffer, "%s", sym_name);

	if (lookup_symbol_name(wchan, symname) < 0)

		return sprintf(buffer, "%lu", wchan);

	else

		return sprintf(buffer, "%s", symname);

}

#endif /* CONFIG_KALLSYMS */

include/linux/kallsyms.h

+7 −0
Original line number Diff line number Diff line
@@ -30,6 +30,8 @@ extern int sprint_symbol(char *buffer, unsigned long address); 
/* Look up a kernel symbol and print it to the kernel messages. */

extern void __print_symbol(const char *fmt, unsigned long address);



int lookup_symbol_name(unsigned long addr, char *symname);



#else /* !CONFIG_KALLSYMS */



static inline unsigned long kallsyms_lookup_name(const char *name)
@@ -58,6 +60,11 @@ static inline int sprint_symbol(char *buffer, unsigned long addr) 
	return 0;

}



static inline int lookup_symbol_name(unsigned long addr, char *symname)

{

	return -ERANGE;

}



/* Stupid that this does nothing, but I didn't create this mess. */

#define __print_symbol(fmt, addr)

#endif /*CONFIG_KALLSYMS*/

include/linux/module.h

+6 −0
Original line number Diff line number Diff line
@@ -454,6 +454,7 @@ const char *module_address_lookup(unsigned long addr, 
				  unsigned long *symbolsize,

				  unsigned long *offset,

				  char **modname);

int lookup_module_symbol_name(unsigned long addr, char *symname);



/* For extable.c to search modules' exception tables. */

const struct exception_table_entry *search_module_extables(unsigned long addr);
@@ -525,6 +526,11 @@ static inline const char *module_address_lookup(unsigned long addr, 
	return NULL;

}



static inline int lookup_module_symbol_name(unsigned long addr, char *symname)

{

	return -ERANGE;

}



static inline int module_get_kallsym(unsigned int symnum, unsigned long *value,

					char *type, char *name,

					char *module_name, int *exported)

kernel/kallsyms.c

+17 −0
Original line number Diff line number Diff line
@@ -269,6 +269,23 @@ const char *kallsyms_lookup(unsigned long addr, 
	return NULL;

}



int lookup_symbol_name(unsigned long addr, char *symname)

{

	symname[0] = '\0';

	symname[KSYM_NAME_LEN] = '\0';



	if (is_ksym_addr(addr)) {

		unsigned long pos;



		pos = get_symbol_pos(addr, NULL, NULL);

		/* Grab name */

		kallsyms_expand_symbol(get_symbol_offset(pos), symname);

		return 0;

	}

	/* see if it's in a module */

	return lookup_module_symbol_name(addr, symname);

}



/* Look up a kernel symbol and return it in a text buffer. */

int sprint_symbol(char *buffer, unsigned long address)

{

kernel/module.c

+23 −0
Original line number Diff line number Diff line
@@ -2126,6 +2126,29 @@ const char *module_address_lookup(unsigned long addr, 
	return NULL;

}



int lookup_module_symbol_name(unsigned long addr, char *symname)

{

	struct module *mod;



	mutex_lock(&module_mutex);

	list_for_each_entry(mod, &modules, list) {

		if (within(addr, mod->module_init, mod->init_size) ||

		    within(addr, mod->module_core, mod->core_size)) {

			const char *sym;



			sym = get_ksymbol(mod, addr, NULL, NULL);

			if (!sym)

				goto out;

			strlcpy(symname, sym, KSYM_NAME_LEN + 1);

			mutex_unlock(&module_mutex);

			return 0;

		}

	}

out:

	mutex_unlock(&module_mutex);

	return -ERANGE;

}



int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,

			char *name, char *module_name, int *exported)

{

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