From: Waiman Long longman@redhat.com
[ Upstream commit d4eaa2837851db2bfed572898bfc17f9a9f9151e ]
For kvmalloc'ed data object that contains sensitive information like cryptographic keys, we need to make sure that the buffer is always cleared before freeing it. Using memset() alone for buffer clearing may not provide certainty as the compiler may compile it away. To be sure, the special memzero_explicit() has to be used.
This patch introduces a new kvfree_sensitive() for freeing those sensitive data objects allocated by kvmalloc(). The relevant places where kvfree_sensitive() can be used are modified to use it.
Fixes: 4f0882491a14 ("KEYS: Avoid false positive ENOMEM error on key read") Suggested-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Waiman Long longman@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Eric Biggers ebiggers@google.com Acked-by: David Howells dhowells@redhat.com Cc: Jarkko Sakkinen jarkko.sakkinen@linux.intel.com Cc: James Morris jmorris@namei.org Cc: "Serge E. Hallyn" serge@hallyn.com Cc: Joe Perches joe@perches.com Cc: Matthew Wilcox willy@infradead.org Cc: David Rientjes rientjes@google.com Cc: Uladzislau Rezki urezki@gmail.com Link: http://lkml.kernel.org/r/20200407200318.11711-1-longman@redhat.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/mm.h | 1 + mm/util.c | 18 ++++++++++++++++++ security/keys/internal.h | 11 ----------- security/keys/keyctl.c | 16 +++++----------- 4 files changed, 24 insertions(+), 22 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index 53bad834adf5..3285dae06c03 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -694,6 +694,7 @@ static inline void *kvcalloc(size_t n, size_t size, gfp_t flags) }
extern void kvfree(const void *addr); +extern void kvfree_sensitive(const void *addr, size_t len);
/* * Mapcount of compound page as a whole, does not include mapped sub-pages. diff --git a/mm/util.c b/mm/util.c index 3ad6db9a722e..ab358c64bbd3 100644 --- a/mm/util.c +++ b/mm/util.c @@ -594,6 +594,24 @@ void kvfree(const void *addr) } EXPORT_SYMBOL(kvfree);
+/** + * kvfree_sensitive - Free a data object containing sensitive information. + * @addr: address of the data object to be freed. + * @len: length of the data object. + * + * Use the special memzero_explicit() function to clear the content of a + * kvmalloc'ed object containing sensitive data to make sure that the + * compiler won't optimize out the data clearing. + */ +void kvfree_sensitive(const void *addr, size_t len) +{ + if (likely(!ZERO_OR_NULL_PTR(addr))) { + memzero_explicit((void *)addr, len); + kvfree(addr); + } +} +EXPORT_SYMBOL(kvfree_sensitive); + static inline void *__page_rmapping(struct page *page) { unsigned long mapping; diff --git a/security/keys/internal.h b/security/keys/internal.h index 7e9914943616..1ca8bfaed0e8 100644 --- a/security/keys/internal.h +++ b/security/keys/internal.h @@ -350,15 +350,4 @@ static inline void key_check(const struct key *key) #define key_check(key) do {} while(0)
#endif - -/* - * Helper function to clear and free a kvmalloc'ed memory object. - */ -static inline void __kvzfree(const void *addr, size_t len) -{ - if (addr) { - memset((void *)addr, 0, len); - kvfree(addr); - } -} #endif /* _INTERNAL_H */ diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c index 5e01192e222a..edde63a63007 100644 --- a/security/keys/keyctl.c +++ b/security/keys/keyctl.c @@ -142,10 +142,7 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type,
key_ref_put(keyring_ref); error3: - if (payload) { - memzero_explicit(payload, plen); - kvfree(payload); - } + kvfree_sensitive(payload, plen); error2: kfree(description); error: @@ -360,7 +357,7 @@ long keyctl_update_key(key_serial_t id,
key_ref_put(key_ref); error2: - __kvzfree(payload, plen); + kvfree_sensitive(payload, plen); error: return ret; } @@ -914,7 +911,7 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen) */ if (ret > key_data_len) { if (unlikely(key_data)) - __kvzfree(key_data, key_data_len); + kvfree_sensitive(key_data, key_data_len); key_data_len = ret; continue; /* Allocate buffer */ } @@ -923,7 +920,7 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen) ret = -EFAULT; break; } - __kvzfree(key_data, key_data_len); + kvfree_sensitive(key_data, key_data_len);
key_put_out: key_put(key); @@ -1225,10 +1222,7 @@ long keyctl_instantiate_key_common(key_serial_t id, keyctl_change_reqkey_auth(NULL);
error2: - if (payload) { - memzero_explicit(payload, plen); - kvfree(payload); - } + kvfree_sensitive(payload, plen); error: return ret; }