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Commit 8d0086ad authored by Gerrit Renker's avatar Gerrit Renker Committed by Arnaldo Carvalho de Melo
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[DCCP] tfrc: Add protection against invalid parameters to TFRC routines 



 1) For the forward X_calc lookup, it
    * protects effectively against RTT=0 (this case is possible), by
      returning the maximal lookup value instead of just setting it to 1
    * reformulates the array-bounds exceeded condition: this only happens
      if p is greater than 1E6 (due to the scaling)
    * the case of negative indices can now with certainty be excluded,
      since documentation shows that the formulas are within bounds
    * additional protection against p = 0 (would give divide-by-zero)

 2) For the reverse lookup, it warns against
    * protects against exceeding array bounds
    * now returns 0 if f(p) = 0, due to function definition
    * warns about minimal resolution error and returns the smallest table
      value instead of p=0 [this would mask congestion conditions]

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@mandriva.com>
parent 90fb0e60

net/dccp/ccids/lib/tfrc_equation.c

+19 −14
Original line number Diff line number Diff line
@@ -608,22 +608,19 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p) 
	u32 f;

	u64 tmp1, tmp2;



	/* check against invalid parameters and divide-by-zero   */

	BUG_ON(p >  1000000);		/* p must not exceed 100%   */

	BUG_ON(p == 0);			/* f(0) = 0, divide by zero */

	if (R == 0) {			/* possible  divide by zero */

		DCCP_CRIT("WARNING: RTT is 0, returning maximum X_calc.");

		return ~0U;

 	}



	if (p < TFRC_CALC_X_SPLIT) 		      /* 0      <= p <  0.05  */

		index = (p / (TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE)) - 1;

	else		 			      /* 0.05   <= p <= 1.00  */

		index = (p / (1000000 / TFRC_CALC_X_ARRSIZE)) - 1;



	if (index < 0)

		/* p should be 0 unless there is a bug in my code */

		index = 0;



	if (R == 0) {

		DCCP_WARN("RTT==0, setting to 1\n");

		R = 1; /* RTT can't be zero or else divide by zero */

	}



	BUG_ON(index >= TFRC_CALC_X_ARRSIZE);



	if (p >= TFRC_CALC_X_SPLIT)

		f = tfrc_calc_x_lookup[index][0];

	else
@@ -653,13 +650,21 @@ u32 tfrc_calc_x_reverse_lookup(u32 fvalue) 
	int ctr = 0;

	int small;



	if (fvalue < tfrc_calc_x_lookup[0][1])

	if (fvalue == 0)	/* f(p) = 0  whenever  p = 0 */

		return 0;



	/* Error cases. */

	if (fvalue < tfrc_calc_x_lookup[0][1]) {

		DCCP_WARN("fvalue %d smaller than resolution\n", fvalue);

		return tfrc_calc_x_lookup[0][1];

	}

	if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) {

		DCCP_WARN("fvalue %d exceeds bounds!\n", fvalue);

		return 1000000;

	}



	if (fvalue <= tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][1])

		small = 1;

	else if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0])

		return 1000000;

	else

		small = 0;