This commit fixes issue #1212 related to platform-specific entropy
polling in an syscall-emulated environment.
Previously, the implementation of the entropy gathering function
`mbedtls_platform_entropy_poll()` for linux machines used the
following logic to determine how to obtain entropy from the kernel:
1. If the getrandom() system call identifier SYS_getrandom is present and
the kernel version is 3.17 or higher, use syscall( SYS_getrandom, ... )
2. Otherwise, fall back to reading from /dev/random.
There are two issues with this:
1. Portability:
When cross-compiling the code for a different
architecture and running it through system call
emulation in qemu, qemu reports the host kernel
version through uname but, as of v.2.5.0,
doesn't support emulating the getrandom() syscall.
This leads to `mbedtls_platform_entropy_poll()`
failing even though reading from /dev/random would
have worked.
2. Style:
Extracting the linux kernel version from
the output of `uname` is slightly tedious.
This commit fixes both by implementing the suggestion in #1212:
- It removes the kernel-version detection through uname().
- Instead, it checks whether `syscall( SYS_getrandom, ... )`
fails with errno set to ENOSYS indicating an unknown system call.
If so, it falls through to trying to read from /dev/random.
Fixes#1212.
This commit changes the behavior of the record decryption routine
`ssl_decrypt_buf()` in the following situation:
1. A CBC ciphersuite with Encrypt-then-MAC is used.
2. A record with valid MAC but invalid CBC padding is received.
In this situation, the previous code would not raise and error but
instead forward the decrypted packet, including the wrong padding,
to the user.
This commit changes this behavior to return the error
MBEDTLS_ERR_SSL_INVALID_MAC instead.
While erroneous, the previous behavior does not constitute a
security flaw since it can only happen for properly authenticated
records, that is, if the peer makes a mistake while preparing the
padded plaintext.
`mbedtls_ssl_get_record_expansion()` is supposed to return the maximum
difference between the size of a protected record and the size of the
encapsulated plaintext.
Previously, it did not correctly estimate the maximum record expansion
in case of CBC ciphersuites in (D)TLS versions 1.1 and higher, in which
case the ciphertext is prefixed by an explicit IV.
This commit fixes this bug. Fixes#1914.
In `mbedtls_ccm_self_test()`, enforce input and output
buffers sent to the ccm API to be contigous and aligned,
by copying the test vectors to buffers on the stack.
- in x509_profile_check_pk_alg
- in x509_profile_check_md_alg
- in x509_profile_check_key
and in ssl_cli.c : unsigned char gets promoted to signed integer
In ecp_mul_comb(), if (!p_eq_g && grp->T == NULL) and then ecp_precompute_comb() fails (which can
happen due to OOM), then the new array of points T will be leaked (as it's newly allocated, but
hasn't been asigned to grp->T yet).
Symptom was a memory leak in ECDHE key exchange under low memory conditions.
The length to the debug message could conceivably leak through the time it
takes to print it, and that length would in turn reveal whether padding was
correct or not.
The basis for the Lucky 13 family of attacks is for an attacker to be able to
distinguish between (long) valid TLS-CBC padding and invalid TLS-CBC padding.
Since our code sets padlen = 0 for invalid padding, the length of the input to
the HMAC function, and the location where we read the MAC, give information
about that.
A local attacker could gain information about that by observing via a
cache attack whether the bytes at the end of the record (at the location of
would-be padding) have been read during MAC verification (computation +
comparison).
Let's make sure they're always read.
The basis for the Lucky 13 family of attacks is for an attacker to be able to
distinguish between (long) valid TLS-CBC padding and invalid TLS-CBC padding.
Since our code sets padlen = 0 for invalid padding, the length of the input to
the HMAC function gives information about that.
Information about this length (modulo the MD/SHA block size) can be deduced
from how much MD/SHA padding (this is distinct from TLS-CBC padding) is used.
If MD/SHA padding is read from a (static) buffer, a local attacker could get
information about how much is used via a cache attack targeting that buffer.
Let's get rid of this buffer. Now the only buffer used is the internal MD/SHA
one, which is always read fully by the process() function.
Move definition of `MBEDTLS_CIPHER_MODE_STREAM` to header file
(`mbedtls_cipher_internal.h`), because it is used by more than
one file. Raised by TrinityTonic in #1719
