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authorLinus Torvalds <torvalds@linux-foundation.org>2020-08-07 13:24:58 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-07 13:24:58 -0700
commit6ba0d2e4fc2f3e8544f40fb1165c668f78fe951c (patch)
treef2b8cc2350bcccb8129e6b1f36b648daa9631c75 /kernel/module.c
parent1fa2c0a0c814fbae0eb3e79a510765225570d043 (diff)
parent9af47666cb0f331bfcd76799ee368cdfcb00882c (diff)
Merge tag 'kallsyms_show_value-fix-v5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
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
Diffstat (limited to 'kernel/module.c')
-rw-r--r--kernel/module.c22
1 files changed, 19 insertions, 3 deletions
diff --git a/kernel/module.c b/kernel/module.c
index e7b4ff7e4fd0..8fa2600bde6a 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -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;
}