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[DCCP] tfrc: Add protection against invalid parameters to TFRC routines

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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: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
This commit is contained in:
Gerrit Renker 2006-12-03 14:52:26 -02:00 committed by Arnaldo Carvalho de Melo
parent 90fb0e60dd
commit 8d0086adac
1 changed files with 19 additions and 14 deletions
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33
net/dccp/ccids/lib/tfrc_equation.c
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@ -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;