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Make sure that shared memory object name meets the length requirements (
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#64099) (#64266)

Co-authored-by: Stephen Toub <stoub@microsoft.com>
# Conflicts:
#	src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFile.CreateNew.Tests.cs
#	src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewAccessor.Tests.cs
#	src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewStream.Tests.cs
#	src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedViewStreamConformanceTests.cs
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adamsitnik authored Feb 7, 2022
1 parent 2caf6fb commit 2168e52
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Showing 6 changed files with 42 additions and 20 deletions.
6 changes: 6 additions & 0 deletions src/libraries/Native/Unix/System.Native/pal_io.c
Original file line number Diff line number Diff line change
Expand Up @@ -324,6 +324,12 @@ int32_t SystemNative_Unlink(const char* path)

intptr_t SystemNative_ShmOpen(const char* name, int32_t flags, int32_t mode)
{
#if defined(SHM_NAME_MAX) // macOS
assert(strlen(name) <= SHM_NAME_MAX);
#elif defined(PATH_MAX) // other Unixes
assert(strlen(name) <= PATH_MAX);
#endif

#if HAVE_SHM_OPEN_THAT_WORKS_WELL_ENOUGH_WITH_MMAP
flags = ConvertOpenFlags(flags);
if (flags == -1)
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@@ -1,6 +1,7 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Diagnostics;
using Microsoft.Win32.SafeHandles;

namespace System.IO.MemoryMappedFiles
Expand Down Expand Up @@ -173,9 +174,6 @@ private static FileStream CreateSharedBackingObject(Interop.Sys.MemoryMappedProt
private static FileStream? CreateSharedBackingObjectUsingMemory(
Interop.Sys.MemoryMappedProtections protections, long capacity, HandleInheritability inheritability)
{
// The POSIX shared memory object name must begin with '/'. After that we just want something short and unique.
string mapName = string.Create(null, stackalloc char[128], $"/corefx_map_{Guid.NewGuid():N}");

// Determine the flags to use when creating the shared memory object
Interop.Sys.OpenFlags flags = (protections & Interop.Sys.MemoryMappedProtections.PROT_WRITE) != 0 ?
Interop.Sys.OpenFlags.O_RDWR :
Expand All @@ -191,22 +189,32 @@ private static FileStream CreateSharedBackingObject(Interop.Sys.MemoryMappedProt
if ((protections & Interop.Sys.MemoryMappedProtections.PROT_EXEC) != 0)
perms |= Interop.Sys.Permissions.S_IXUSR;

// Create the shared memory object.
SafeFileHandle fd = Interop.Sys.ShmOpen(mapName, flags, (int)perms);
if (fd.IsInvalid)
string mapName;
SafeFileHandle fd;

do
{
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
if (errorInfo.Error == Interop.Error.ENOTSUP)
mapName = GenerateMapName();
fd = Interop.Sys.ShmOpen(mapName, flags, (int)perms); // Create the shared memory object.

if (fd.IsInvalid)
{
// If ShmOpen is not supported, fall back to file backing object.
// Note that the System.Native shim will force this failure on platforms where
// the result of native shm_open does not work well with our subsequent call
// to mmap.
return null;
}
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
fd.Dispose();

throw Interop.GetExceptionForIoErrno(errorInfo);
}
if (errorInfo.Error == Interop.Error.ENOTSUP)
{
// If ShmOpen is not supported, fall back to file backing object.
// Note that the System.Native shim will force this failure on platforms where
// the result of native shm_open does not work well with our subsequent call to mmap.
return null;
}
else if (errorInfo.Error != Interop.Error.EEXIST) // map with same name already existed
{
throw Interop.GetExceptionForIoErrno(errorInfo);
}
}
} while (fd.IsInvalid);

try
{
Expand Down Expand Up @@ -236,6 +244,18 @@ private static FileStream CreateSharedBackingObject(Interop.Sys.MemoryMappedProt
fd.Dispose();
throw;
}

static string GenerateMapName()
{
const int MaxSharedMemoryObjectNameLength = 32; // SHM_NAME_MAX on OSX ARM64, on other systems it's equal PATH_MAX (250)
// The POSIX shared memory object name must begin with '/'. After that we just want something short (32) and unique.
return string.Create(MaxSharedMemoryObjectNameLength, 0, (span, state) =>
{
Guid.NewGuid().TryFormat(span, out int charsWritten, "N");
Debug.Assert(charsWritten == MaxSharedMemoryObjectNameLength);
"/dotnet_".CopyTo(span);
});
}
}

private static FileStream CreateSharedBackingObjectUsingFile(Interop.Sys.MemoryMappedProtections protections, long capacity, HandleInheritability inheritability)
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,6 @@ namespace System.IO.MemoryMappedFiles.Tests
/// <summary>
/// Tests for MemoryMappedFile.CreateNew.
/// </summary>
[ActiveIssue("https://github.com/dotnet/runtime/issues/49104", typeof(PlatformDetection), nameof(PlatformDetection.IsMacOsAppleSilicon))]
public class MemoryMappedFileTests_CreateNew : MemoryMappedFilesTestBase
{
/// <summary>
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,6 @@ namespace System.IO.MemoryMappedFiles.Tests
/// <summary>
/// Tests for MemoryMappedViewAccessor.
/// </summary>
[ActiveIssue("https://github.com/dotnet/runtime/issues/49104", typeof(PlatformDetection), nameof(PlatformDetection.IsMacOsAppleSilicon))]
public class MemoryMappedViewAccessorTests : MemoryMappedFilesTestBase
{
/// <summary>
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,6 @@ namespace System.IO.MemoryMappedFiles.Tests
/// <summary>
/// Tests for MemoryMappedViewStream.
/// </summary>
[ActiveIssue("https://github.com/dotnet/runtime/issues/49104", typeof(PlatformDetection), nameof(PlatformDetection.IsMacOsAppleSilicon))]
public class MemoryMappedViewStreamTests : MemoryMappedFilesTestBase
{
/// <summary>
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,6 @@ private Task<Stream> CreateStream(byte[] initialData, FileAccess access)
}
}

[ActiveIssue("https://github.com/dotnet/runtime/issues/49104", typeof(PlatformDetection), nameof(PlatformDetection.IsMacOsAppleSilicon))]
public class AnonymousMemoryMappedViewStreamConformanceTests : MemoryMappedViewStreamConformanceTests
{
protected override MemoryMappedFile CreateFile(int length) =>
Expand Down

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