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authorWaiman Long <longman@redhat.com>2020-03-21 21:11:25 -0400
committerDavid Howells <dhowells@redhat.com>2020-03-29 12:40:41 +0100
commit4f0882491a148059a52480e753b7f07fc550e188 (patch)
tree5f8861f74d8324e66056e5af33209b3d23f50f90
parentd3ec10aa95819bff18a0d936b18884c7816d0914 (diff)
downloadlinux-stericsson-4f0882491a148059a52480e753b7f07fc550e188.tar.gz
KEYS: Avoid false positive ENOMEM error on key read
By allocating a kernel buffer with a user-supplied buffer length, it is possible that a false positive ENOMEM error may be returned because the user-supplied length is just too large even if the system do have enough memory to hold the actual key data. Moreover, if the buffer length is larger than the maximum amount of memory that can be returned by kmalloc() (2^(MAX_ORDER-1) number of pages), a warning message will also be printed. To reduce this possibility, we set a threshold (PAGE_SIZE) over which we do check the actual key length first before allocating a buffer of the right size to hold it. The threshold is arbitrary, it is just used to trigger a buffer length check. It does not limit the actual key length as long as there is enough memory to satisfy the memory request. To further avoid large buffer allocation failure due to page fragmentation, kvmalloc() is used to allocate the buffer so that vmapped pages can be used when there is not a large enough contiguous set of pages available for allocation. In the extremely unlikely scenario that the key keeps on being changed and made longer (still <= buflen) in between 2 __keyctl_read_key() calls, the __keyctl_read_key() calling loop in keyctl_read_key() may have to be iterated a large number of times, but definitely not infinite. Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com>
-rw-r--r--security/keys/internal.h12
-rw-r--r--security/keys/keyctl.c58
2 files changed, 55 insertions, 15 deletions
diff --git a/security/keys/internal.h b/security/keys/internal.h
index ba3e2da14cef..6d0ca48ae9a5 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -16,6 +16,8 @@
#include <linux/keyctl.h>
#include <linux/refcount.h>
#include <linux/compat.h>
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
struct iovec;
@@ -349,4 +351,14 @@ static inline void key_check(const struct key *key)
#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 434ed9defd3a..0062e422e0fd 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -339,7 +339,7 @@ long keyctl_update_key(key_serial_t id,
payload = NULL;
if (plen) {
ret = -ENOMEM;
- payload = kmalloc(plen, GFP_KERNEL);
+ payload = kvmalloc(plen, GFP_KERNEL);
if (!payload)
goto error;
@@ -360,7 +360,7 @@ long keyctl_update_key(key_serial_t id,
key_ref_put(key_ref);
error2:
- kzfree(payload);
+ __kvzfree(payload, plen);
error:
return ret;
}
@@ -827,7 +827,8 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
struct key *key;
key_ref_t key_ref;
long ret;
- char *key_data;
+ char *key_data = NULL;
+ size_t key_data_len;
/* find the key first */
key_ref = lookup_user_key(keyid, 0, 0);
@@ -878,24 +879,51 @@ can_read_key:
* Allocating a temporary buffer to hold the keys before
* transferring them to user buffer to avoid potential
* deadlock involving page fault and mmap_sem.
+ *
+ * key_data_len = (buflen <= PAGE_SIZE)
+ * ? buflen : actual length of key data
+ *
+ * This prevents allocating arbitrary large buffer which can
+ * be much larger than the actual key length. In the latter case,
+ * at least 2 passes of this loop is required.
*/
- key_data = kmalloc(buflen, GFP_KERNEL);
+ key_data_len = (buflen <= PAGE_SIZE) ? buflen : 0;
+ for (;;) {
+ if (key_data_len) {
+ key_data = kvmalloc(key_data_len, GFP_KERNEL);
+ if (!key_data) {
+ ret = -ENOMEM;
+ goto key_put_out;
+ }
+ }
- if (!key_data) {
- ret = -ENOMEM;
- goto key_put_out;
- }
- ret = __keyctl_read_key(key, key_data, buflen);
+ ret = __keyctl_read_key(key, key_data, key_data_len);
+
+ /*
+ * Read methods will just return the required length without
+ * any copying if the provided length isn't large enough.
+ */
+ if (ret <= 0 || ret > buflen)
+ break;
+
+ /*
+ * The key may change (unlikely) in between 2 consecutive
+ * __keyctl_read_key() calls. In this case, we reallocate
+ * a larger buffer and redo the key read when
+ * key_data_len < ret <= buflen.
+ */
+ if (ret > key_data_len) {
+ if (unlikely(key_data))
+ __kvzfree(key_data, key_data_len);
+ key_data_len = ret;
+ continue; /* Allocate buffer */
+ }
- /*
- * Read methods will just return the required length without
- * any copying if the provided length isn't large enough.
- */
- if (ret > 0 && ret <= buflen) {
if (copy_to_user(buffer, key_data, ret))
ret = -EFAULT;
+ break;
}
- kzfree(key_data);
+ __kvzfree(key_data, key_data_len);
key_put_out:
key_put(key);