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[XPCOM] Compare return value of readlink in nsLocalFileUnix::GetNativeTarget

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This commit is contained in:
Barret Rennie 2023-12-20 18:33:23 +01:00 • committed by roytam1
commit 8b5c0a9cd9
1 changed files with 46 additions and 24 deletions
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70
xpcom/io/nsLocalFileUnix.cpp
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@ -1699,6 +1699,47 @@ nsLocalFile::Contains(nsIFile* aInFile, bool* aResult)
return NS_OK;
}
static nsresult ReadLinkSafe(const nsCString& aTarget, int32_t aExpectedSize,
nsACString& aOutBuffer) {
// If we call readlink with a buffer size S it returns S, then we cannot tell
// if the buffer was big enough to hold the entire path. We allocate an
// additional byte so we can check if the buffer was large enough.
const auto allocSize = CheckedInt<size_t>(aExpectedSize) + 1;
if (!allocSize.isValid()) {
return NS_ERROR_OUT_OF_MEMORY;
}
auto result = aOutBuffer.BulkWrite(allocSize.value(), 0, false);
if (result.isErr()) {
return result.unwrapErr();
}
auto handle = result.unwrap();
while (true) {
ssize_t bytesWritten =
readlink(aTarget.get(), handle.Elements(), handle.Length());
if (bytesWritten < 0) {
return NSRESULT_FOR_ERRNO();
}
// written >= 0 so it is safe to cast to size_t.
if ((size_t)bytesWritten < handle.Length()) {
// Target might have changed since the lstat call, or lstat might lie, see
// bug 1791029.
handle.Finish(bytesWritten, false);
return NS_OK;
}
// The buffer was not large enough, so double it and try again.
auto restartResult = handle.RestartBulkWrite(handle.Length() * 2, 0, false);
if (restartResult.isErr()) {
return restartResult.unwrapErr();
}
}
}
NS_IMETHODIMP
nsLocalFile::GetNativeTarget(nsACString& aResult)
{
@ -1714,21 +1755,12 @@ nsLocalFile::GetNativeTarget(nsACString& aResult)
return NS_ERROR_FILE_INVALID_PATH;
}
int32_t size = (int32_t)symStat.st_size;
nsAutoCString target;
if (!target.SetLength(size, mozilla::fallible)) {
return NS_ERROR_OUT_OF_MEMORY;
nsresult rv = ReadLinkSafe(mPath, symStat.st_size, target);
if (NS_FAILED(rv)) {
return rv;
}
ssize_t written = readlink(mPath.get(), target.BeginWriting(), size_t(size));
if (written < 0) {
return NSRESULT_FOR_ERRNO();
}
// Target might have changed since the lstat call, or lstat might lie, see bug
// 1791029.
target.Truncate(written);
nsresult rv = NS_OK;
nsCOMPtr<nsIFile> self(this);
int32_t maxLinks = 40;
while (true) {
@ -1766,22 +1798,12 @@ nsLocalFile::GetNativeTarget(nsACString& aResult)
break;
}
int32_t newSize = (int32_t)symStat.st_size;
size = newSize;
nsAutoCString newTarget;
if (!newTarget.SetLength(size, mozilla::fallible)) {
rv = NS_ERROR_OUT_OF_MEMORY;
rv = ReadLinkSafe(flatRetval, symStat.st_size, newTarget);
if (NS_FAILED(rv)) {
break;
}
ssize_t linkLen = readlink(flatRetval.get(), newTarget.BeginWriting(), size);
if (linkLen == -1) {
rv = NSRESULT_FOR_ERRNO();
break;
}
// Target might have changed since the lstat call, or lstat might lie, see bug
// 1791029.
newTarget.Truncate(linkLen);
target = newTarget;
}