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Fix potential stack underflow in mpi_read_file.

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When provided with an empty line, mpi_read_file causes a numeric
underflow resulting in a stack underflow. This commit fixes this and
adds some documentation to mpi_read_file.
This commit is contained in:
Hanno Becker 2017-05-12 07:26:01 +01:00
parent 98864d5c0b
commit 8c7698b62a
3 changed files with 18 additions and 4 deletions
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6
ChangeLog
View file

@ -1,5 +1,11 @@
mbed TLS ChangeLog (Sorted per branch, date)
= mbed TLS x.x.x branch released xxxx-xx-xx
Bugfix
* Fix potential stack underflow in mpi_read_file.
Found by Guido Vranken.
= mbed TLS 1.3.19 branch released 2017-03-08
Security

10
include/polarssl/bignum.h
View file

@ -377,7 +377,7 @@ int mpi_write_string( const mpi *X, int radix, char *s, size_t *slen );
#if defined(POLARSSL_FS_IO)
/**
* \brief Read X from an opened file
* \brief Read MPI from a line in an opened file
*
* \param X Destination MPI
* \param radix Input numeric base
@ -386,6 +386,14 @@ int mpi_write_string( const mpi *X, int radix, char *s, size_t *slen );
* \return 0 if successful, POLARSSL_ERR_MPI_BUFFER_TOO_SMALL if
* the file read buffer is too small or a
* POLARSSL_ERR_MPI_XXX error code
*
* \note On success, this function advances the file stream
* to the end of the current line or to EOF.
*
* The function returns 0 on an empty line.
*
* Leading whitespaces are ignored, as is a
* '0x' prefix for radix 16.
*/
int mpi_read_file( mpi *X, int radix, FILE *fin );

6
library/bignum.c
View file

@ -620,11 +620,11 @@ int mpi_read_file( mpi *X, int radix, FILE *fin )
if( slen == sizeof( s ) - 2 )
return( POLARSSL_ERR_MPI_BUFFER_TOO_SMALL );
if( s[slen - 1] == '\n' ) { slen--; s[slen] = '\0'; }
if( s[slen - 1] == '\r' ) { slen--; s[slen] = '\0'; }
if( slen > 0 && s[slen - 1] == '\n' ) { slen--; s[slen] = '\0'; }
if( slen > 0 && s[slen - 1] == '\r' ) { slen--; s[slen] = '\0'; }
p = s + slen;
while( --p >= s )
while( p-- > s )
if( mpi_get_digit( &d, radix, *p ) != 0 )
break;