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Merge tag 'kallsyms_show_value-fix-v5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

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Pull sysfs module section fix from Kees Cook:
 "Fix sysfs module section output overflow.

  About a month after my kallsyms_show_value() refactoring landed, 0day
  noticed that there was a path through the kernfs binattr read handlers
  that did not have PAGE_SIZEd buffers, and the module "sections" read
  handler made a bad assumption about this, resulting in it stomping on
  memory when reached through small-sized splice() calls.

  I've added a set of tests to find these kinds of regressions more
  quickly in the future as well"

Sefltests-acked-by: Shuah Khan <skhan@linuxfoundation.org>

* tag 'kallsyms_show_value-fix-v5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  selftests: splice: Check behavior of full and short splices
  module: Correctly truncate sysfs sections output
This commit is contained in:
Linus Torvalds
2020-08-07 13:24:58 -07:00
parent 1fa2c0a0c8 9af47666cb
commit 6ba0d2e4fc
7 changed files with 137 additions and 5 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[];
};
#define MODULE_SECT_READ_SIZE (3 /* "0x", "\n" */ + (BITS_PER_LONG / 4))
static ssize_t module_sect_read(struct file *file, struct kobject *kobj,
struct bin_attribute *battr,
char *buf, loff_t pos, size_t count)
{
struct module_sect_attr *sattr =
container_of(battr, struct module_sect_attr, battr);
char bounce[MODULE_SECT_READ_SIZE + 1];
size_t wrote;
if (pos != 0)
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)
@@ -1580,7 +1596,7 @@ static void add_sect_attrs(struct module *mod, const struct load_info *info)
goto out;
sect_attrs->nsections++;
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;
*(gattr++) = &(sattr++)->battr;
}