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Always check if block is last in linked list before consuming it 

- This prevents a race where we could read into the "Next" Block without
  completely consuming the previous one.
This commit is contained in:
Stephen Halter 2016-05-04 16:45:59 -07:00
parent faf81f11f5
commit 4c39374dc0
1 changed files with 47 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

74
src/Microsoft.AspNetCore.Server.Kestrel/Infrastructure/MemoryPoolIterator.cs
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@ -68,6 +68,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
} }
var index = _index; var index = _index;
var wasLastBlock = block.Next == null;
if (index < block.End) if (index < block.End)
{ {
@ -77,7 +78,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
do do
{ {
if (block.Next == null) if (wasLastBlock)
{ {
return -1; return -1;
} }
@ -87,6 +88,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
index = block.Start; index = block.Start;
} }
wasLastBlock = block.Next == null;
if (index < block.End) if (index < block.End)
{ {
_block = block; _block = block;
@ -102,7 +105,10 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
{ {
return; return;
} }
var wasLastBlock = _block.Next == null;
var following = _block.End - _index; var following = _block.End - _index;
if (following >= bytesToSkip) if (following >= bytesToSkip)
{ {
_index += bytesToSkip; _index += bytesToSkip;
@ -113,7 +119,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
var index = _index; var index = _index;
while (true) while (true)
{ {
if (block.Next == null) if (wasLastBlock)
{ {
return; return;
} }
@ -123,7 +129,10 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
block = block.Next; block = block.Next;
index = block.Start; index = block.Start;
} }
wasLastBlock = block.Next == null;
following = block.End - index; following = block.End - index;
if (following >= bytesToSkip) if (following >= bytesToSkip)
{ {
_block = block; _block = block;
@ -141,6 +150,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
return -1; return -1;
} }
var wasLastBlock = _block.Next == null;
var index = _index; var index = _index;
if (index < block.End) if (index < block.End)
@ -150,7 +160,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
do do
{ {
if (block.Next == null) if (wasLastBlock)
{ {
return -1; return -1;
} }
@ -160,6 +170,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
index = block.Start; index = block.Start;
} }
wasLastBlock = block.Next == null;
if (index < block.End) if (index < block.End)
{ {
return block.Array[index]; return block.Array[index];
@ -173,14 +185,17 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
{ {
return -1; return -1;
} }
else if (_block.End - _index >= sizeof(long))
var wasLastBlock = _block.Next == null;
if (_block.End - _index >= sizeof(long))
{ {
fixed (byte* ptr = &_block.Array[_index]) fixed (byte* ptr = &_block.Array[_index])
{ {
return *(long*)(ptr); return *(long*)(ptr);
} }
} }
else if (_block.Next == null) else if (wasLastBlock)
{ {
return -1; return -1;
} }
@ -219,6 +234,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
var block = _block; var block = _block;
var index = _index; var index = _index;
var wasLastBlock = block.Next == null;
var following = block.End - index; var following = block.End - index;
byte[] array; byte[] array;
var byte0 = byte0Vector[0]; var byte0 = byte0Vector[0];
@ -227,16 +243,16 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
{ {
while (following == 0) while (following == 0)
{ {
var newBlock = block.Next; if (wasLastBlock)
if (newBlock == null)
{ {
_block = block; _block = block;
_index = index; _index = index;
return -1; return -1;
} }
index = newBlock.Start; block = block.Next;
following = newBlock.End - index; index = block.Start;
block = newBlock; wasLastBlock = block.Next == null;
following = block.End - index;
} }
array = block.Array; array = block.Array;
while (following > 0) while (following > 0)
@ -298,6 +314,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
var block = _block; var block = _block;
var index = _index; var index = _index;
var wasLastBlock = block.Next == null;
var following = block.End - index; var following = block.End - index;
byte[] array; byte[] array;
int byte0Index = int.MaxValue; int byte0Index = int.MaxValue;
@ -309,16 +326,16 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
{ {
while (following == 0) while (following == 0)
{ {
var newBlock = block.Next; if (wasLastBlock)
if (newBlock == null)
{ {
_block = block; _block = block;
_index = index; _index = index;
return -1; return -1;
} }
index = newBlock.Start; block = block.Next;
following = newBlock.End - index; index = block.Start;
block = newBlock; wasLastBlock = block.Next == null;
following = block.End - index;
} }
array = block.Array; array = block.Array;
while (following > 0) while (following > 0)
@ -405,6 +422,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
var block = _block; var block = _block;
var index = _index; var index = _index;
var wasLastBlock = block.Next == null;
var following = block.End - index; var following = block.End - index;
byte[] array; byte[] array;
int byte0Index = int.MaxValue; int byte0Index = int.MaxValue;
@ -418,16 +436,16 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
{ {
while (following == 0) while (following == 0)
{ {
var newBlock = block.Next; if (wasLastBlock)
if (newBlock == null)
{ {
_block = block; _block = block;
_index = index; _index = index;
return -1; return -1;
} }
index = newBlock.Start; block = block.Next;
following = newBlock.End - index; index = block.Start;
block = newBlock; wasLastBlock = block.Next == null;
following = block.End - index;
} }
array = block.Array; array = block.Array;
while (following > 0) while (following > 0)
@ -605,16 +623,13 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
{ {
return false; return false;
} }
else if (_index < _block.End)
{
_block.Array[_index++] = data;
return true;
}
var block = _block; var block = _block;
var index = _index; var index = _index;
while (true) while (true)
{ {
var wasLastBlock = block.Next == null;
if (index < block.End) if (index < block.End)
{ {
_block = block; _block = block;
@ -622,7 +637,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
block.Array[index] = data; block.Array[index] = data;
return true; return true;
} }
else if (block.Next == null) else if (wasLastBlock)
{ {
return false; return false;
} }
@ -679,6 +694,11 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
var remaining = count; var remaining = count;
while (true) while (true)
{ {
// Determine if we might attempt to copy data from block.Next before
// calculating "following" so we don't risk skipping data that could
// be added after block.End when we decide to copy from block.Next.
// block.End will always be advanced before block.Next is set.
var wasLastBlock = block.Next == null;
var following = block.End - index; var following = block.End - index;
if (remaining <= following) if (remaining <= following)
{ {
@ -689,7 +709,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Infrastructure
} }
return new MemoryPoolIterator(block, index + remaining); return new MemoryPoolIterator(block, index + remaining);
} }
else if (block.Next == null) else if (wasLastBlock)
{ {
actual = count - remaining + following; actual = count - remaining + following;
if (array != null) if (array != null)