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module: Correctly truncate sysfs sections output

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The only-root-readable /sys/module/$module/sections/$section files
did not truncate their output to the available buffer size. While most
paths into the kernfs read handlers end up using PAGE_SIZE buffers,
it's possible to get there through other paths (e.g. splice, sendfile).
Actually limit the output to the "count" passed into the read function,
and report it back correctly. *sigh*

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/20200805002015.GE23458@shao2-debian
Fixes: ed66f991bb ("module: Refactor section attr into bin attribute")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2020-08-06 14:15:23 -07:00
parent bcf876870b
commit 11990a5bd7
1 changed files with 19 additions and 3 deletions
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22
kernel/module.c
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@ -1520,18 +1520,34 @@ struct module_sect_attrs {
struct module_sect_attr attrs[]; struct module_sect_attr attrs[];
}; };
#define MODULE_SECT_READ_SIZE (3 /* "0x", "\n" */ + (BITS_PER_LONG / 4))
static ssize_t module_sect_read(struct file *file, struct kobject *kobj, static ssize_t module_sect_read(struct file *file, struct kobject *kobj,
struct bin_attribute *battr, struct bin_attribute *battr,
char *buf, loff_t pos, size_t count) char *buf, loff_t pos, size_t count)
{ {
struct module_sect_attr *sattr = struct module_sect_attr *sattr =
container_of(battr, struct module_sect_attr, battr); container_of(battr, struct module_sect_attr, battr);
char bounce[MODULE_SECT_READ_SIZE + 1];
size_t wrote;
if (pos != 0) if (pos != 0)
return -EINVAL; return -EINVAL;
return sprintf(buf, "0x%px\n", /*
kallsyms_show_value(file->f_cred) ? (void *)sattr->address : NULL); * Since we're a binary read handler, we must account for the
* trailing NUL byte that sprintf will write: if "buf" is
* too small to hold the NUL, or the NUL is exactly the last
* byte, the read will look like it got truncated by one byte.
* Since there is no way to ask sprintf nicely to not write
* the NUL, we have to use a bounce buffer.
*/
wrote = scnprintf(bounce, sizeof(bounce), "0x%px\n",
kallsyms_show_value(file->f_cred)
? (void *)sattr->address : NULL);
count = min(count, wrote);
memcpy(buf, bounce, count);
return count;
} }
static void free_sect_attrs(struct module_sect_attrs *sect_attrs) static void free_sect_attrs(struct module_sect_attrs *sect_attrs)
@ -1580,7 +1596,7 @@ static void add_sect_attrs(struct module *mod, const struct load_info *info)
goto out; goto out;
sect_attrs->nsections++; sect_attrs->nsections++;
sattr->battr.read = module_sect_read; sattr->battr.read = module_sect_read;
sattr->battr.size = 3 /* "0x", "\n" */ + (BITS_PER_LONG / 4); sattr->battr.size = MODULE_SECT_READ_SIZE;
sattr->battr.attr.mode = 0400; sattr->battr.attr.mode = 0400;
*(gattr++) = &(sattr++)->battr; *(gattr++) = &(sattr++)->battr;
} }