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GET /api/patches/2224035/?format=api
{ "id": 2224035, "url": "http://patchwork.ozlabs.org/api/patches/2224035/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-cifs-client/patch/20260416151839.3315696-1-charsyam@gmail.com/", "project": { "id": 12, "url": "http://patchwork.ozlabs.org/api/projects/12/?format=api", "name": "Linux CIFS Client", "link_name": "linux-cifs-client", "list_id": "linux-cifs.vger.kernel.org", "list_email": "linux-cifs@vger.kernel.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260416151839.3315696-1-charsyam@gmail.com>", "list_archive_url": null, "date": "2026-04-16T15:18:39", "name": "[v2] smb/client: fix chan_max and UNC state corruption in smb3_reconfigure", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "cd012cc86eb974c3a396bbab4bf83faf901f4e9c", "submitter": { "id": 93166, "url": "http://patchwork.ozlabs.org/api/people/93166/?format=api", "name": "CharSyam", "email": "charsyam@gmail.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/linux-cifs-client/patch/20260416151839.3315696-1-charsyam@gmail.com/mbox/", "series": [ { "id": 500178, "url": "http://patchwork.ozlabs.org/api/series/500178/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-cifs-client/list/?series=500178", "date": "2026-04-16T15:18:39", "name": "[v2] smb/client: fix chan_max and UNC state corruption in smb3_reconfigure", "version": 2, "mbox": "http://patchwork.ozlabs.org/series/500178/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2224035/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2224035/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "\n <linux-cifs+bounces-10864-incoming=patchwork.ozlabs.org@vger.kernel.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "linux-cifs@vger.kernel.org" ], "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=EM3OZla3;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=172.105.105.114; helo=tor.lore.kernel.org;\n envelope-from=linux-cifs+bounces-10864-incoming=patchwork.ozlabs.org@vger.kernel.org;\n receiver=patchwork.ozlabs.org)", "smtp.subspace.kernel.org;\n\tdkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com\n header.b=\"EM3OZla3\"", "smtp.subspace.kernel.org;\n arc=none smtp.client-ip=209.85.214.182", "smtp.subspace.kernel.org;\n dmarc=pass (p=none dis=none) header.from=gmail.com", "smtp.subspace.kernel.org;\n spf=pass smtp.mailfrom=gmail.com" ], "Received": [ "from tor.lore.kernel.org (tor.lore.kernel.org [172.105.105.114])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fxMDC4YDqz1yCv\n\tfor <incoming@patchwork.ozlabs.org>; Fri, 17 Apr 2026 01:21:15 +1000 (AEST)", "from smtp.subspace.kernel.org (conduit.subspace.kernel.org\n [100.90.174.1])\n\tby tor.lore.kernel.org (Postfix) with ESMTP id 90DC7306D1E2\n\tfor <incoming@patchwork.ozlabs.org>; Thu, 16 Apr 2026 15:18:54 +0000 (UTC)", "from localhost.localdomain (localhost.localdomain [127.0.0.1])\n\tby smtp.subspace.kernel.org (Postfix) with ESMTP id CF6D43E3C5A;\n\tThu, 16 Apr 2026 15:18:53 +0000 (UTC)", "from mail-pl1-f182.google.com (mail-pl1-f182.google.com\n [209.85.214.182])\n\t(using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))\n\t(No client certificate requested)\n\tby smtp.subspace.kernel.org (Postfix) with ESMTPS id 66C2C3E3C5E\n\tfor <linux-cifs@vger.kernel.org>; Thu, 16 Apr 2026 15:18:48 +0000 (UTC)", "by mail-pl1-f182.google.com with SMTP id\n d9443c01a7336-2a8720818aeso9085095ad.1\n for <linux-cifs@vger.kernel.org>;\n Thu, 16 Apr 2026 08:18:48 -0700 (PDT)", "from ser8.. 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If a concurrent operation (e.g.\n smb2_reconnect) holds the flag, the current thread takes the\n loser path and returns -EINVAL, but ses->chan_max has already\n been updated to the new value. chan_max is then inconsistent\n with the actual channel state.\n\n2) When smb3_update_ses_channels() fails, ses->chan_max is not\n rolled back and the error is not propagated to the caller.\n mount returns success even though the channel configuration\n was not applied, and repeated failures cause chan_max to\n drift further from reality.\n\n3) Earlier in smb3_reconfigure(), STEAL_STRING moves UNC, source\n and username from cifs_sb->ctx into ctx, setting\n cifs_sb->ctx->UNC to NULL until smb3_fs_context_dup() copies\n them back near the end of the function. Both the existing\n CIFS_SES_FLAG_SCALE_CHANNELS loser-path 'return -EINVAL' and a\n naive 'if (rc < 0) return rc;' to propagate the failure above\n exit in this window. A single failed multichannel remount\n therefore permanently nulls cifs_sb->ctx->UNC; /proc/mounts\n shows the device as \"none\" and every subsequent\n mount.cifs-based remount is rejected by\n smb3_verify_reconfigure_ctx() because mount.cifs passes that\n \"none\" back as the new UNC.\n\n4) If the multichannel update fails but smb3_fs_context_dup() is\n still allowed to run with the new ctx values, the rejected\n new max_channels is written into cifs_sb->ctx, undoing the\n ses->chan_max rollback from (2) and creating a fresh\n cifs_sb->ctx vs ses->chan_max mismatch.\n\nFix all four by:\n - Moving smb3_sync_ses_chan_max() after the SCALE_CHANNELS\n acquire so the loser path cannot corrupt chan_max.\n - Capturing old_chan_max before the sync and restoring it on\n failure while still holding SCALE_CHANNELS so a concurrent\n reconfigure cannot race with the rollback.\n - Recording any multichannel-path failure in a local mchan_rc\n and routing it through a common 'out:' label so every exit\n reaches smb3_fs_context_dup() and cifs_sb->ctx is restored.\n - Before the dup, restoring ctx->multichannel and\n ctx->max_channels from cifs_sb->ctx on mchan_rc so the dup\n does not desync cifs_sb->ctx from the already-rolled-back\n ses->chan_max.\n - Returning mchan_rc to userspace so a failed scaling remount\n surfaces as an error.\n - Surfacing smb3_fs_context_dup() failure in preference to\n mchan_rc when both occur. The dup is the final step of the\n ctx restore and runs after smb3_cleanup_fs_context_contents()\n has already freed cifs_sb->ctx's strings, so a dup failure\n (e.g. -ENOMEM) leaves cifs_sb->ctx partially restored with\n some strings still NULL. Reporting the scaling error in that\n case would hide the real recovery status from userspace;\n reporting the dup error exposes it so the caller can react\n accordingly.\n\nNote: smb3_reconfigure() is not fully transactional. Credentials\n(ses->password and ses->password2) are committed before the\nmultichannel block, so a failed multichannel remount can still\nleave ses->password updated while reporting an error to\nuserspace. Making the entire function atomic is a larger\nrefactor and is left for a separate patch.\n\nTested with a QEMU VM (ksmbd + cifs) using module-parameter-based\nfault injection:\n - Forced smb3_update_ses_channels() failure via module param\n and verified ses->chan_max is preserved at the old value\n after remount failure.\n - Pre-set CIFS_SES_FLAG_SCALE_CHANNELS before entering the\n scaling path and verified the loser path returns -EINVAL\n without corrupting ses->chan_max.\n - Repeated 19 forced-failure remounts with varying max_channels\n (range 2-8) and confirmed no chan_max drift.\n - After each failure path, verified /proc/mounts continues to\n show the original UNC (//127.0.0.1/share) so subsequent\n remounts are accepted.\nAll scenarios pass with the patch and fail without it.\n\nReported-by: RAJASI MANDAL <rajasimandalos@gmail.com>\nCloses: https://lore.kernel.org/lkml/CAEY6_V1+dzW3OD5zqXhsWyXwrDTrg5tAMGZ1AJ7_GAuRE+aevA@mail.gmail.com/\nFixes: ef529f655a2c (\"cifs: client: allow changing multichannel mount options on remount\")\nSigned-off-by: DaeMyung Kang <charsyam@gmail.com>\n---\n fs/smb/client/fs_context.c | 48 ++++++++++++++++++++++++++++++++------\n 1 file changed, 41 insertions(+), 7 deletions(-)", "diff": "diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c\nindex b9544eb0381b..9efd73ce6910 100644\n--- a/fs/smb/client/fs_context.c\n+++ b/fs/smb/client/fs_context.c\n@@ -1085,10 +1085,11 @@ static int smb3_reconfigure(struct fs_context *fc)\n \tstruct dentry *root = fc->root;\n \tstruct cifs_sb_info *cifs_sb = CIFS_SB(root->d_sb);\n \tstruct cifs_ses *ses = cifs_sb_master_tcon(cifs_sb)->ses;\n+\tunsigned int old_chan_max;\n \tunsigned int rsize = ctx->rsize, wsize = ctx->wsize;\n \tchar *new_password = NULL, *new_password2 = NULL;\n \tbool need_recon = false;\n-\tint rc;\n+\tint rc, mchan_rc = 0;\n \n \tif (ses->expired_pwd)\n \t\tneed_recon = true;\n@@ -1170,25 +1171,37 @@ static int smb3_reconfigure(struct fs_context *fc)\n \tif ((ctx->multichannel != cifs_sb->ctx->multichannel) ||\n \t (ctx->max_channels != cifs_sb->ctx->max_channels)) {\n \n-\t\t/* Synchronize ses->chan_max with the new mount context */\n-\t\tsmb3_sync_ses_chan_max(ses, ctx->max_channels);\n-\t\t/* Now update the session's channels to match the new configuration */\n \t\t/* Prevent concurrent scaling operations */\n \t\tspin_lock(&ses->ses_lock);\n \t\tif (ses->flags & CIFS_SES_FLAG_SCALE_CHANNELS) {\n \t\t\tspin_unlock(&ses->ses_lock);\n \t\t\tmutex_unlock(&ses->session_mutex);\n-\t\t\treturn -EINVAL;\n+\t\t\tmchan_rc = -EINVAL;\n+\t\t\tgoto out;\n \t\t}\n \t\tses->flags |= CIFS_SES_FLAG_SCALE_CHANNELS;\n \t\tspin_unlock(&ses->ses_lock);\n \n+\t\told_chan_max = ses->chan_max;\n+\t\t/* Synchronize ses->chan_max with the new mount context */\n+\t\tsmb3_sync_ses_chan_max(ses, ctx->max_channels);\n+\n \t\tmutex_unlock(&ses->session_mutex);\n \n \t\trc = smb3_update_ses_channels(ses, ses->server,\n \t\t\t\t\t false /* from_reconnect */,\n \t\t\t\t\t false /* disable_mchan */);\n \n+\t\t/*\n+\t\t * On failure, restore chan_max while still holding\n+\t\t * CIFS_SES_FLAG_SCALE_CHANNELS so a concurrent reconfigure\n+\t\t * cannot observe or race with the rollback.\n+\t\t */\n+\t\tif (rc < 0) {\n+\t\t\tsmb3_sync_ses_chan_max(ses, old_chan_max);\n+\t\t\tmchan_rc = rc;\n+\t\t}\n+\n \t\t/* Clear scaling flag after operation */\n \t\tspin_lock(&ses->ses_lock);\n \t\tses->flags &= ~CIFS_SES_FLAG_SCALE_CHANNELS;\n@@ -1197,6 +1210,7 @@ static int smb3_reconfigure(struct fs_context *fc)\n \t\tmutex_unlock(&ses->session_mutex);\n \t}\n \n+out:\n \tSTEAL_STRING(cifs_sb, ctx, domainname);\n \tSTEAL_STRING(cifs_sb, ctx, nodename);\n \tSTEAL_STRING(cifs_sb, ctx, iocharset);\n@@ -1205,12 +1219,32 @@ static int smb3_reconfigure(struct fs_context *fc)\n \tctx->rsize = rsize ? CIFS_ALIGN_RSIZE(fc, rsize) : cifs_sb->ctx->rsize;\n \tctx->wsize = wsize ? CIFS_ALIGN_WSIZE(fc, wsize) : cifs_sb->ctx->wsize;\n \n+\t/*\n+\t * If the multichannel update failed, restore the old multichannel\n+\t * settings in ctx so smb3_fs_context_dup() does not desync\n+\t * cifs_sb->ctx from ses->chan_max (which was already rolled back).\n+\t */\n+\tif (mchan_rc) {\n+\t\tctx->multichannel = cifs_sb->ctx->multichannel;\n+\t\tctx->max_channels = cifs_sb->ctx->max_channels;\n+\t}\n+\n \tsmb3_cleanup_fs_context_contents(cifs_sb->ctx);\n \trc = smb3_fs_context_dup(cifs_sb->ctx, ctx);\n \tsmb3_update_mnt_flags(cifs_sb);\n+\n+\t/*\n+\t * If smb3_fs_context_dup() failed, cifs_sb->ctx is left in a\n+\t * partially-restored state after the cleanup above. Surface that\n+\t * failure to the caller before any mchan_rc, since it reflects the\n+\t * real recovery status of cifs_sb->ctx rather than the scaling error.\n+\t */\n+\tif (rc)\n+\t\treturn rc;\n+\tif (mchan_rc)\n+\t\treturn mchan_rc;\n #ifdef CONFIG_CIFS_DFS_UPCALL\n-\tif (!rc)\n-\t\trc = dfs_cache_remount_fs(cifs_sb);\n+\trc = dfs_cache_remount_fs(cifs_sb);\n #endif\n \n \treturn rc;\n", "prefixes": [ "v2" ] }